diff --git a/applications/solvers/multiphase/compressibleInterFoam/twoPhaseMixtureThermo/twoPhaseMixtureThermo.H b/applications/solvers/multiphase/compressibleInterFoam/twoPhaseMixtureThermo/twoPhaseMixtureThermo.H
index c712e5a47f..9209cc41d2 100644
--- a/applications/solvers/multiphase/compressibleInterFoam/twoPhaseMixtureThermo/twoPhaseMixtureThermo.H
+++ b/applications/solvers/multiphase/compressibleInterFoam/twoPhaseMixtureThermo/twoPhaseMixtureThermo.H
@@ -135,14 +135,14 @@ public:
             virtual volScalarField& he()
             {
                 NotImplemented;
-                return thermo1_->he();
+                return const_cast<volScalarField&>(volScalarField::null());
             }
 
             //- Enthalpy/Internal energy [J/kg]
             virtual const volScalarField& he() const
             {
                 NotImplemented;
-                return thermo1_->he();
+                return volScalarField::null();
             }
 
             //- Enthalpy/Internal energy
@@ -213,7 +213,7 @@ public:
             ) const
             {
                 NotImplemented;
-                return tmp<scalarField>::New(p);
+                return nullptr;
             }
 
             //- Heat capacity at constant volume [J/kg/K]
@@ -236,7 +236,7 @@ public:
             ) const
             {
                 NotImplemented;
-                return tmp<scalarField>::New(p);
+                return nullptr;
             }
 
             //- Gamma = Cp/Cv []
diff --git a/applications/solvers/multiphase/compressibleMultiphaseInterFoam/multiphaseMixtureThermo/multiphaseMixtureThermo.H b/applications/solvers/multiphase/compressibleMultiphaseInterFoam/multiphaseMixtureThermo/multiphaseMixtureThermo.H
index 472bd285aa..c5e90dada5 100644
--- a/applications/solvers/multiphase/compressibleMultiphaseInterFoam/multiphaseMixtureThermo/multiphaseMixtureThermo.H
+++ b/applications/solvers/multiphase/compressibleMultiphaseInterFoam/multiphaseMixtureThermo/multiphaseMixtureThermo.H
@@ -243,14 +243,14 @@ public:
             virtual volScalarField& he()
             {
                 NotImplemented;
-                return phases_[0].thermo().he();
+                return const_cast<volScalarField&>(volScalarField::null());
             }
 
             //- Enthalpy/Internal energy [J/kg]
             virtual const volScalarField& he() const
             {
                 NotImplemented;
-                return phases_[0].thermo().he();
+                return volScalarField::null();
             }
 
             //- Enthalpy/Internal energy
@@ -327,7 +327,7 @@ public:
             ) const
             {
                 NotImplemented;
-                return tmp<scalarField>::New(p);
+                return nullptr;
             }
 
             //- Heat capacity at constant volume [J/kg/K]
@@ -350,7 +350,7 @@ public:
             ) const
             {
                 NotImplemented;
-                return tmp<scalarField>::New(p);
+                return nullptr;
             }
 
             //- Gamma = Cp/Cv []
diff --git a/applications/solvers/multiphase/interCondensatingEvaporatingFoam/temperaturePhaseChangeTwoPhaseMixtures/twoPhaseMixtureEThermo/twoPhaseMixtureEThermo.H b/applications/solvers/multiphase/interCondensatingEvaporatingFoam/temperaturePhaseChangeTwoPhaseMixtures/twoPhaseMixtureEThermo/twoPhaseMixtureEThermo.H
index cedad45329..ab5b58febe 100644
--- a/applications/solvers/multiphase/interCondensatingEvaporatingFoam/temperaturePhaseChangeTwoPhaseMixtures/twoPhaseMixtureEThermo/twoPhaseMixtureEThermo.H
+++ b/applications/solvers/multiphase/interCondensatingEvaporatingFoam/temperaturePhaseChangeTwoPhaseMixtures/twoPhaseMixtureEThermo/twoPhaseMixtureEThermo.H
@@ -86,14 +86,14 @@ public:
         virtual volScalarField& he()
         {
             NotImplemented;
-            return p();
+            return const_cast<volScalarField&>(volScalarField::null());
         }
 
         //- Return access to the internal energy field [J/Kg]
         virtual const volScalarField& he() const
         {
             NotImplemented;
-            return p();
+            return volScalarField::null();
         }
 
         //- Enthalpy/Internal energy
@@ -182,7 +182,7 @@ public:
         ) const
         {
             NotImplemented;
-            return tmp<scalarField>::New(p);
+            return nullptr;
         }
 
         //- Return Cv of the mixture
@@ -205,7 +205,7 @@ public:
         ) const
         {
             NotImplemented;
-            return tmp<scalarField>::New(p);
+            return nullptr;
         }
 
         //- Gamma = Cp/Cv []
diff --git a/applications/test/nullObject/Test-nullObject.C b/applications/test/nullObject/Test-nullObject.C
index 5c86e4e500..0f7cd10dad 100644
--- a/applications/test/nullObject/Test-nullObject.C
+++ b/applications/test/nullObject/Test-nullObject.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2014 OpenFOAM Foundation
-    Copyright (C) 2019-2020 OpenCFD Ltd.
+    Copyright (C) 2019-2024 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -48,7 +48,7 @@ class SimpleClass
 public:
 
     //- Default construct
-    SimpleClass() {}
+    SimpleClass() = default;
 };
 
 
@@ -73,9 +73,8 @@ void printInfo(const UList<T>& list)
 int main()
 {
     // Test pointer and reference to a class
-
-    SimpleClass* ptrToClass = new SimpleClass;
-    SimpleClass& refToClass(*ptrToClass);
+    auto ptrToClass = autoPtr<SimpleClass>::New();
+    auto& refToClass = ptrToClass.ref();
 
     std::cout
         << "nullObject addr=" << name(&(nullObjectPtr)) << nl
@@ -89,13 +88,13 @@ int main()
         << "  pointer:" << name(nullObjectPtr->pointer()) << nl
         << "  value:"   << nullObjectPtr->value() << nl << nl;
 
-    if (notNull(ptrToClass))
+    if (notNull(ptrToClass.get()))
     {
         Info<< "Pass: ptrToClass is not null" << nl;
     }
     else
     {
-        Info<< "FAIL: refToClass is null" << nl;
+        Info<< "FAIL: ptrToClass is null" << nl;
     }
 
     if (notNull(refToClass))
@@ -110,8 +109,8 @@ int main()
 
     // Test pointer and reference to the nullObject
 
-    const SimpleClass* ptrToNull(NullObjectPtr<SimpleClass>());
-    const SimpleClass& refToNull(*ptrToNull);
+    const SimpleClass* ptrToNull = NullObjectPtr<SimpleClass>();
+    const SimpleClass& refToNull = (*ptrToNull);
 
     if (isNull(ptrToNull))
     {
@@ -131,9 +130,6 @@ int main()
         Info<< "FAIL: refToNull is not null" << nl;
     }
 
-    // Clean-up
-    delete ptrToClass;
-
 
     // Test List casting
     {
@@ -152,7 +148,7 @@ int main()
     // Looks pretty ugly though!
 
     NullObject::nullObject = "hello world";
-    NullObject::nullObject = labelList({1, 2, 3});
+    NullObject::nullObject = Foam::identity(5);
 
     Info<< nl;
 
diff --git a/src/OpenFOAM/containers/Bits/bitSet/bitSet.H b/src/OpenFOAM/containers/Bits/bitSet/bitSet.H
index 31d08d570f..b1e4c7fdd4 100644
--- a/src/OpenFOAM/containers/Bits/bitSet/bitSet.H
+++ b/src/OpenFOAM/containers/Bits/bitSet/bitSet.H
@@ -120,8 +120,11 @@ public:
 
     // Static Member Functions
 
-        //- Return a null bitSet reference
-        inline static const bitSet& null();
+        //- Return a null bitSet (reference to a nullObject).
+        static const bitSet& null() noexcept
+        {
+            return NullObjectRef<bitSet>();
+        }
 
 
     //- Declare type-name (with debug switch)
diff --git a/src/OpenFOAM/containers/Bits/bitSet/bitSetI.H b/src/OpenFOAM/containers/Bits/bitSet/bitSetI.H
index 7e9eed8739..f035d0c99f 100644
--- a/src/OpenFOAM/containers/Bits/bitSet/bitSetI.H
+++ b/src/OpenFOAM/containers/Bits/bitSet/bitSetI.H
@@ -405,12 +405,6 @@ inline Foam::label Foam::bitSet::find_next(label pos) const
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
-inline const Foam::bitSet& Foam::bitSet::null()
-{
-    return NullObjectRef<bitSet>();
-}
-
-
 inline bool Foam::bitSet::all() const
 {
     if (empty()) return true;  // SIC. boost convention
diff --git a/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.H b/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.H
index 3401179116..7935b876a2 100644
--- a/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.H
+++ b/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.H
@@ -138,8 +138,11 @@ public:
 
     // Static Member Functions
 
-        //- Return a CompactListList reference to a nullObject
-        inline static const CompactListList<T>& null();
+        //- Return a null CompactListList (reference to a nullObject).
+        static const CompactListList<T>& null() noexcept
+        {
+            return NullObjectRef<CompactListList<T>>();
+        }
 
         //- Construct by packing together the list of lists
         template<class SubListType = List<T>>
diff --git a/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListListI.H b/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListListI.H
index f5a17ba86d..5e5209fcb9 100644
--- a/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListListI.H
+++ b/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListListI.H
@@ -29,15 +29,6 @@ License
 #include "ListOps.H"
 #include "SubList.H"
 
-// * * * * * * * * * * * * * Static Member Functions * * * * * * * * * * * * //
-
-template<class T>
-inline const Foam::CompactListList<T>& Foam::CompactListList<T>::null()
-{
-    return NullObjectRef<CompactListList<T>>();
-}
-
-
 // * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
 template<class T>
diff --git a/src/OpenFOAM/containers/Lists/FixedList/FixedList.H b/src/OpenFOAM/containers/Lists/FixedList/FixedList.H
index 59e1188bee..1c1f8c8476 100644
--- a/src/OpenFOAM/containers/Lists/FixedList/FixedList.H
+++ b/src/OpenFOAM/containers/Lists/FixedList/FixedList.H
@@ -46,9 +46,10 @@ SourceFiles
 #include "zero.H"
 #include "contiguous.H"
 #include "stdFoam.H"
-#include "autoPtr.H"
+#include "nullObject.H"
 #include "Hash.H"
 #include "ListPolicy.H"
+#include "autoPtr.H"
 
 // <algorithm> already included by stdFoam.H
 #include <iterator>
@@ -139,8 +140,12 @@ public:
 
     // Static Functions
 
-        //- Return a null FixedList
-        inline static const FixedList<T, N>& null();
+        //- Return a null FixedList (reference to a nullObject).
+        //- Read/write access is questionable
+        static const FixedList<T, N>& null() noexcept
+        {
+            return NullObjectRef<FixedList<T, N>>();
+        }
 
 
     // Constructors
diff --git a/src/OpenFOAM/containers/Lists/FixedList/FixedListI.H b/src/OpenFOAM/containers/Lists/FixedList/FixedListI.H
index 4bef6f07b3..7d590c3799 100644
--- a/src/OpenFOAM/containers/Lists/FixedList/FixedListI.H
+++ b/src/OpenFOAM/containers/Lists/FixedList/FixedListI.H
@@ -28,15 +28,6 @@ License
 
 #include "UList.H"
 
-// * * * * * * * * * * * * * Static Member Functions * * * * * * * * * * * * //
-
-template<class T, unsigned N>
-inline const Foam::FixedList<T, N>& Foam::FixedList<T, N>::null()
-{
-    return NullObjectRef<FixedList<T, N>>();
-}
-
-
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
 template<class T, unsigned N>
diff --git a/src/OpenFOAM/containers/Lists/List/List.H b/src/OpenFOAM/containers/Lists/List/List.H
index 65caab9fd8..87b9bf9019 100644
--- a/src/OpenFOAM/containers/Lists/List/List.H
+++ b/src/OpenFOAM/containers/Lists/List/List.H
@@ -129,8 +129,12 @@ public:
 
     // Static Member Functions
 
-        //- Return a null List
-        inline static const List<T>& null();
+        //- Return a null List (reference to a nullObject).
+        //- Behaves like an empty List.
+        static const List<T>& null() noexcept
+        {
+            return NullObjectRef<List<T>>();
+        }
 
 
     // Constructors
diff --git a/src/OpenFOAM/containers/Lists/List/ListI.H b/src/OpenFOAM/containers/Lists/List/ListI.H
index 6bab28191b..5bac2f0ee4 100644
--- a/src/OpenFOAM/containers/Lists/List/ListI.H
+++ b/src/OpenFOAM/containers/Lists/List/ListI.H
@@ -133,13 +133,6 @@ inline Foam::autoPtr<Foam::List<T>> Foam::List<T>::clone() const
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
-template<class T>
-inline const Foam::List<T>& Foam::List<T>::null()
-{
-    return NullObjectRef<List<T>>();
-}
-
-
 template<class T>
 inline void Foam::List<T>::clear()
 {
diff --git a/src/OpenFOAM/containers/Lists/List/SubList.H b/src/OpenFOAM/containers/Lists/List/SubList.H
index e34f27fcd0..42f2a1dcd6 100644
--- a/src/OpenFOAM/containers/Lists/List/SubList.H
+++ b/src/OpenFOAM/containers/Lists/List/SubList.H
@@ -73,8 +73,12 @@ public:
 
     // Static Functions
 
-        //- Return a null SubList
-        inline static const SubList<T>& null();
+        //- Return a null SubList (reference to a nullObject).
+        //- Behaves like an empty SubList.
+        static const SubList<T>& null() noexcept
+        {
+            return NullObjectRef<SubList<T>>();
+        }
 
 
     // Generated Methods
diff --git a/src/OpenFOAM/containers/Lists/List/SubListI.H b/src/OpenFOAM/containers/Lists/List/SubListI.H
index 3b15f4c9e1..f18c31646b 100644
--- a/src/OpenFOAM/containers/Lists/List/SubListI.H
+++ b/src/OpenFOAM/containers/Lists/List/SubListI.H
@@ -28,15 +28,6 @@ License
 
 #include "FixedList.H"
 
-// * * * * * * * * * * * * * Static Member Functions * * * * * * * * * * * * //
-
-template<class T>
-inline const Foam::SubList<T>& Foam::SubList<T>::null()
-{
-    return NullObjectRef<SubList<T>>();
-}
-
-
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
 template<class T>
@@ -124,7 +115,7 @@ inline Foam::SubList<T>::SubList
 template<class T>
 inline Foam::UList<T>& Foam::SubList<T>::reset(std::nullptr_t) noexcept
 {
-    UList<T>::shallowCopy(nullptr, 0);
+    UList<T>::shallowCopy(nullptr);
     return *this;
 }
 
diff --git a/src/OpenFOAM/containers/Lists/List/UList.H b/src/OpenFOAM/containers/Lists/List/UList.H
index 252ec61cc3..ceb50199c5 100644
--- a/src/OpenFOAM/containers/Lists/List/UList.H
+++ b/src/OpenFOAM/containers/Lists/List/UList.H
@@ -183,8 +183,12 @@ public:
 
     // Static Functions
 
-        //- Return a UList reference to a nullObject
-        inline static const UList<T>& null();
+        //- Return a null UList (reference to a nullObject).
+        //- Behaves like an empty UList.
+        static const UList<T>& null() noexcept
+        {
+            return NullObjectRef<UList<T>>();
+        }
 
 
     // Public Classes
@@ -367,6 +371,9 @@ public:
         //- Copy the pointer and size
         inline void shallowCopy(T* __restrict__ ptr, const label len) noexcept;
 
+        //- Copy nullptr and zero size
+        inline void shallowCopy(std::nullptr_t) noexcept;
+
         //- Copy the pointer and size held by the given UList
         inline void shallowCopy(const UList<T>& list) noexcept;
 
diff --git a/src/OpenFOAM/containers/Lists/List/UListI.H b/src/OpenFOAM/containers/Lists/List/UListI.H
index b143475599..74cd4c3bbe 100644
--- a/src/OpenFOAM/containers/Lists/List/UListI.H
+++ b/src/OpenFOAM/containers/Lists/List/UListI.H
@@ -93,13 +93,6 @@ inline void Foam::UList<T>::fill_uniform(const Foam::zero)
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
-template<class T>
-inline const Foam::UList<T>& Foam::UList<T>::null()
-{
-    return NullObjectRef<UList<T>>();
-}
-
-
 template<class T>
 inline Foam::label Foam::UList<T>::fcIndex(const label i) const noexcept
 {
@@ -330,6 +323,14 @@ inline void Foam::UList<T>::shallowCopy
 }
 
 
+template<class T>
+inline void Foam::UList<T>::shallowCopy(std::nullptr_t) noexcept
+{
+    size_ = 0;
+    v_ = nullptr;
+}
+
+
 template<class T>
 inline void Foam::UList<T>::shallowCopy(const UList<T>& list) noexcept
 {
diff --git a/src/OpenFOAM/containers/Lists/ListOps/ListOps.C b/src/OpenFOAM/containers/Lists/ListOps/ListOps.C
index 9e4dbd83b7..dd73a69686 100644
--- a/src/OpenFOAM/containers/Lists/ListOps/ListOps.C
+++ b/src/OpenFOAM/containers/Lists/ListOps/ListOps.C
@@ -116,7 +116,7 @@ Foam::labelListList Foam::invertOneToMany
     const labelUList& map
 )
 {
-    labelList sizes(len, Zero);
+    labelList sizes(len, Foam::zero{});
 
     for (const label newIdx : map)
     {
diff --git a/src/OpenFOAM/containers/Lists/ListOps/ListOpsTemplates.C b/src/OpenFOAM/containers/Lists/ListOps/ListOpsTemplates.C
index 4c70358920..e1914040e3 100644
--- a/src/OpenFOAM/containers/Lists/ListOps/ListOpsTemplates.C
+++ b/src/OpenFOAM/containers/Lists/ListOps/ListOpsTemplates.C
@@ -707,7 +707,7 @@ void Foam::invertManyToMany
 )
 {
     // The output list sizes
-    labelList sizes(len, Zero);
+    labelList sizes(len, Foam::zero{});
 
     for (const InputIntListType& sublist : input)
     {
diff --git a/src/OpenFOAM/expressions/Function1/Function1Expression.C b/src/OpenFOAM/expressions/Function1/Function1Expression.C
index dd45c913e7..532344efa8 100644
--- a/src/OpenFOAM/expressions/Function1/Function1Expression.C
+++ b/src/OpenFOAM/expressions/Function1/Function1Expression.C
@@ -115,7 +115,7 @@ Type Foam::Function1Types::Function1Expression<Type>::integrate
 ) const
 {
     NotImplemented;
-    return Zero;
+    return Type();
 }
 
 
diff --git a/src/OpenFOAM/fields/DimensionedFields/DimensionedField/DimensionedField.H b/src/OpenFOAM/fields/DimensionedFields/DimensionedField/DimensionedField.H
index c193f7e176..e7b4d21c6f 100644
--- a/src/OpenFOAM/fields/DimensionedFields/DimensionedField/DimensionedField.H
+++ b/src/OpenFOAM/fields/DimensionedFields/DimensionedField/DimensionedField.H
@@ -137,8 +137,11 @@ public:
 
     // Static Member Functions
 
-        //- Return a NullObjectRef DimensionedField
-        inline static const DimensionedField<Type, GeoMesh>& null();
+        //- Return a null DimensionedField (reference to a nullObject).
+        static const DimensionedField<Type, GeoMesh>& null() noexcept
+        {
+            return NullObjectRef<DimensionedField<Type, GeoMesh>>();
+        }
 
 
     // Constructors
diff --git a/src/OpenFOAM/fields/DimensionedFields/DimensionedField/DimensionedFieldI.H b/src/OpenFOAM/fields/DimensionedFields/DimensionedField/DimensionedFieldI.H
index 5f898c1e6b..3391dc32f4 100644
--- a/src/OpenFOAM/fields/DimensionedFields/DimensionedField/DimensionedFieldI.H
+++ b/src/OpenFOAM/fields/DimensionedFields/DimensionedField/DimensionedFieldI.H
@@ -28,14 +28,6 @@ License
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
-template<class Type, class GeoMesh>
-inline const Foam::DimensionedField<Type, GeoMesh>&
-Foam::DimensionedField<Type, GeoMesh>::null()
-{
-    return NullObjectRef<DimensionedField<Type, GeoMesh>>();
-}
-
-
 template<class Type, class GeoMesh>
 inline const typename GeoMesh::Mesh&
 Foam::DimensionedField<Type, GeoMesh>::mesh() const noexcept
diff --git a/src/OpenFOAM/fields/DimensionedFields/DimensionedField/SlicedDimensionedField.H b/src/OpenFOAM/fields/DimensionedFields/DimensionedField/SlicedDimensionedField.H
index 9f6df361ac..de0eb8a6cc 100644
--- a/src/OpenFOAM/fields/DimensionedFields/DimensionedField/SlicedDimensionedField.H
+++ b/src/OpenFOAM/fields/DimensionedFields/DimensionedField/SlicedDimensionedField.H
@@ -85,7 +85,7 @@ public:
     ~SlicedDimensionedField()
     {
         // Set internalField to nullptr to avoid deletion of underlying field
-        UList<Type>::shallowCopy(UList<Type>());
+        UList<Type>::shallowCopy(nullptr);
     }
 };
 
diff --git a/src/OpenFOAM/fields/Fields/DynamicField/DynamicField.H b/src/OpenFOAM/fields/Fields/DynamicField/DynamicField.H
index 7debed435b..602e6f1cce 100644
--- a/src/OpenFOAM/fields/Fields/DynamicField/DynamicField.H
+++ b/src/OpenFOAM/fields/Fields/DynamicField/DynamicField.H
@@ -97,8 +97,8 @@ public:
 
     // Static Member Functions
 
-        //- Return a null field
-        inline static const DynamicField<T, SizeMin>& null()
+        //- Return a null DynamicField (reference to a nullObject).
+        static const DynamicField<T, SizeMin>& null() noexcept
         {
             return NullObjectRef<DynamicField<T, SizeMin>>();
         }
diff --git a/src/OpenFOAM/fields/Fields/Field/Field.H b/src/OpenFOAM/fields/Fields/Field/Field.H
index 9a2d17c7a4..fb7851edc6 100644
--- a/src/OpenFOAM/fields/Fields/Field/Field.H
+++ b/src/OpenFOAM/fields/Fields/Field/Field.H
@@ -122,8 +122,12 @@ public:
 
     // Static Member Functions
 
-        //- Return nullObject reference Field
-        inline static const Field<Type>& null();
+        //- Return a null Field (reference to a nullObject).
+        //- Behaves like an empty Field.
+        static const Field<Type>& null() noexcept
+        {
+            return NullObjectRef<Field<Type>>();
+        }
 
 
     // Constructors
diff --git a/src/OpenFOAM/fields/Fields/Field/FieldI.H b/src/OpenFOAM/fields/Fields/Field/FieldI.H
index a5c37b841b..4c34df88b1 100644
--- a/src/OpenFOAM/fields/Fields/Field/FieldI.H
+++ b/src/OpenFOAM/fields/Fields/Field/FieldI.H
@@ -25,15 +25,6 @@ License
 
 \*---------------------------------------------------------------------------*/
 
-// * * * * * * * * * * * * * Static Member Functions * * * * * * * * * * * * //
-
-template<class Type>
-inline const Foam::Field<Type>& Foam::Field<Type>::null()
-{
-    return NullObjectRef<Field<Type>>();
-}
-
-
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
 template<class Type>
diff --git a/src/OpenFOAM/fields/Fields/Field/SubField.H b/src/OpenFOAM/fields/Fields/Field/SubField.H
index 48cc8530ff..15e09522a7 100644
--- a/src/OpenFOAM/fields/Fields/Field/SubField.H
+++ b/src/OpenFOAM/fields/Fields/Field/SubField.H
@@ -69,8 +69,12 @@ public:
 
     // Static Member Functions
 
-        //- Return nullObject reference SubField
-        inline static const SubField<Type>& null();
+        //- Return a null SubField (reference to a nullObject).
+        //- Behaves like an empty SubField.
+        static const SubField<Type>& null() noexcept
+        {
+            return NullObjectRef<SubField<Type>>();
+        }
 
 
     // Constructors
diff --git a/src/OpenFOAM/fields/Fields/Field/SubFieldI.H b/src/OpenFOAM/fields/Fields/Field/SubFieldI.H
index 738096e039..235f981da7 100644
--- a/src/OpenFOAM/fields/Fields/Field/SubFieldI.H
+++ b/src/OpenFOAM/fields/Fields/Field/SubFieldI.H
@@ -26,15 +26,6 @@ License
 
 \*---------------------------------------------------------------------------*/
 
-// * * * * * * * * * * * * * Static Member Functions * * * * * * * * * * * * //
-
-template<class Type>
-inline const Foam::SubField<Type>& Foam::SubField<Type>::null()
-{
-    return NullObjectRef<SubField<Type>>();
-}
-
-
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
 template<class Type>
diff --git a/src/OpenFOAM/fields/GeometricFields/GeometricField/GeometricField.H b/src/OpenFOAM/fields/GeometricFields/GeometricField/GeometricField.H
index 8c66779bf2..427009b245 100644
--- a/src/OpenFOAM/fields/GeometricFields/GeometricField/GeometricField.H
+++ b/src/OpenFOAM/fields/GeometricFields/GeometricField/GeometricField.H
@@ -154,8 +154,11 @@ public:
 
     // Static Member Functions
 
-        //- Return a null geometric field
-        inline static const GeometricField<Type, PatchField, GeoMesh>& null();
+        //- Return a null GeometricField (reference to a nullObject).
+        static const GeometricField<Type, PatchField, GeoMesh>& null() noexcept
+        {
+            return NullObjectRef<GeometricField<Type, PatchField, GeoMesh>>();
+        }
 
 
     // Constructors
diff --git a/src/OpenFOAM/fields/GeometricFields/GeometricField/GeometricFieldI.H b/src/OpenFOAM/fields/GeometricFields/GeometricField/GeometricFieldI.H
index 90b57d17a4..0f3083ae48 100644
--- a/src/OpenFOAM/fields/GeometricFields/GeometricField/GeometricFieldI.H
+++ b/src/OpenFOAM/fields/GeometricFields/GeometricField/GeometricFieldI.H
@@ -28,14 +28,6 @@ License
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
-template<class Type, template<class> class PatchField, class GeoMesh>
-inline const Foam::GeometricField<Type, PatchField, GeoMesh>&
-Foam::GeometricField<Type, PatchField, GeoMesh>::null()
-{
-    return NullObjectRef<GeometricField<Type, PatchField, GeoMesh>>();
-}
-
-
 template<class Type, template<class> class PatchField, class GeoMesh>
 inline const typename
 Foam::GeometricField<Type, PatchField, GeoMesh>::Internal&
diff --git a/src/OpenFOAM/fields/GeometricFields/SlicedGeometricField/SlicedGeometricField.C b/src/OpenFOAM/fields/GeometricFields/SlicedGeometricField/SlicedGeometricField.C
index 2b378137fd..f77ccd0bfa 100644
--- a/src/OpenFOAM/fields/GeometricFields/SlicedGeometricField/SlicedGeometricField.C
+++ b/src/OpenFOAM/fields/GeometricFields/SlicedGeometricField/SlicedGeometricField.C
@@ -368,7 +368,7 @@ Foam::SlicedGeometricField<Type, PatchField, SlicedPatchField, GeoMesh>::
 ~SlicedGeometricField()
 {
     // Set internalField to nullptr to avoid deletion of underlying field
-    UList<Type>::shallowCopy(UList<Type>());
+    UList<Type>::shallowCopy(nullptr);
 }
 
 
diff --git a/src/OpenFOAM/matrices/Matrix/Matrix.H b/src/OpenFOAM/matrices/Matrix/Matrix.H
index 7bff0b2a77..cdfa892253 100644
--- a/src/OpenFOAM/matrices/Matrix/Matrix.H
+++ b/src/OpenFOAM/matrices/Matrix/Matrix.H
@@ -114,8 +114,12 @@ public:
 
     // Static Member Functions
 
-        //- Return a null Matrix
-        inline static const Matrix<Form, Type>& null();
+        //- Return a null Matrix (reference to a nullObject).
+        //- Behaves like a empty Matrix.
+        static const Matrix<Form, Type>& null() noexcept
+        {
+            return NullObjectRef<Matrix<Form, Type>>();
+        }
 
 
     // Iterators
diff --git a/src/OpenFOAM/matrices/Matrix/MatrixI.H b/src/OpenFOAM/matrices/Matrix/MatrixI.H
index 17f35969cc..b1dc3b1267 100644
--- a/src/OpenFOAM/matrices/Matrix/MatrixI.H
+++ b/src/OpenFOAM/matrices/Matrix/MatrixI.H
@@ -85,13 +85,6 @@ Foam::Matrix<Form, Type>::clone() const
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
-template<class Form, class Type>
-inline const Foam::Matrix<Form, Type>& Foam::Matrix<Form, Type>::null()
-{
-    return NullObjectRef<Matrix<Form, Type>>();
-}
-
-
 template<class Form, class Type>
 inline Foam::label Foam::Matrix<Form, Type>::size() const
 {
diff --git a/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/interfaceFields/processorCyclicGAMGInterfaceField/processorCyclicGAMGInterfaceField.H b/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/interfaceFields/processorCyclicGAMGInterfaceField/processorCyclicGAMGInterfaceField.H
index 376631dd7d..5096b8cfbb 100644
--- a/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/interfaceFields/processorCyclicGAMGInterfaceField/processorCyclicGAMGInterfaceField.H
+++ b/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/interfaceFields/processorCyclicGAMGInterfaceField/processorCyclicGAMGInterfaceField.H
@@ -102,7 +102,7 @@ public:
         ) const
         {
             NotImplemented;
-            return autoPtr<GAMGInterfaceField>(nullptr);
+            return nullptr;
         }
 
 
diff --git a/src/OpenFOAM/meshes/lduMesh/lduMesh.C b/src/OpenFOAM/meshes/lduMesh/lduMesh.C
index 16e73ddf7c..a6c62c3811 100644
--- a/src/OpenFOAM/meshes/lduMesh/lduMesh.C
+++ b/src/OpenFOAM/meshes/lduMesh/lduMesh.C
@@ -42,8 +42,7 @@ namespace Foam
 const Foam::objectRegistry& Foam::lduMesh::thisDb() const
 {
     NotImplemented;
-    const objectRegistry* orPtr_ = nullptr;
-    return *orPtr_;
+    return NullObjectRef<objectRegistry>();
 }
 
 
diff --git a/src/OpenFOAM/primitives/nullObject/nullObject.H b/src/OpenFOAM/primitives/nullObject/nullObject.H
index 8d3793f50c..f8d1fc269e 100644
--- a/src/OpenFOAM/primitives/nullObject/nullObject.H
+++ b/src/OpenFOAM/primitives/nullObject/nullObject.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2014 OpenFOAM Foundation
-    Copyright (C) 2017-2020 OpenCFD Ltd.
+    Copyright (C) 2017-2024 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -158,7 +158,7 @@ extern const NullObject* nullObjectPtr;
 
 // IOstream Operators
 
-//- Read from Istream consumes no content
+//- Read from Istream consumes no content, does not change NullObject
 inline Istream& operator>>(Istream& is, const NullObject&) noexcept
 {
     return is;
@@ -173,31 +173,48 @@ inline Ostream& operator<<(Ostream& os, const NullObject&) noexcept
 
 // Global Functions
 
-//- Pointer (of type T) to the nullObject
+//- Const pointer (of type T) to the nullObject
 template<class T>
-inline const T* NullObjectPtr()
+inline const T* NullObjectPtr() noexcept
 {
     return reinterpret_cast<const T*>(nullObjectPtr);
 }
 
-//- Reference (of type T) to the nullObject
+//- Non-const pointer (of type T) to the nullObject.
+//- Only use when nothing will be written into it!
 template<class T>
-inline const T& NullObjectRef()
+inline T* NullObjectPtr_constCast() noexcept
+{
+    return reinterpret_cast<T*>(const_cast<NullObject*>(nullObjectPtr));
+}
+
+
+//- Const reference (of type T) to the nullObject
+template<class T>
+inline const T& NullObjectRef() noexcept
 {
     return *reinterpret_cast<const T*>(nullObjectPtr);
 }
 
+//- Non-const reference (of type T) to the nullObject
+//- Only use when nothing will be written into it!
+template<class T>
+inline T& NullObjectRef_constCast() noexcept
+{
+    return *reinterpret_cast<T*>(const_cast<NullObject*>(nullObjectPtr));
+}
+
 
 //- True if ptr is a pointer (of type T) to the nullObject
 template<class T>
-inline bool isNull(const T* ptr)
+inline bool isNull(const T* ptr) noexcept
 {
     return ptr == NullObjectPtr<T>();
 }
 
 //- True if obj is a reference (of type T) to the nullObject
 template<class T>
-inline bool isNull(const T& obj)
+inline bool isNull(const T& obj) noexcept
 {
     return &obj == NullObjectPtr<T>();
 }
@@ -205,14 +222,14 @@ inline bool isNull(const T& obj)
 
 //- True if ptr is not a pointer (of type T) to the nullObject
 template<class T>
-inline bool notNull(const T* ptr)
+inline bool notNull(const T* ptr) noexcept
 {
     return ptr != NullObjectPtr<T>();
 }
 
 //- True if obj is not a reference (of type T) to the nullObject
 template<class T>
-inline bool notNull(const T& obj)
+inline bool notNull(const T& obj) noexcept
 {
     return &obj != NullObjectPtr<T>();
 }
diff --git a/src/OpenFOAM/primitives/strings/wordRes/wordRes.H b/src/OpenFOAM/primitives/strings/wordRes/wordRes.H
index de7c5d56aa..e665f4d52d 100644
--- a/src/OpenFOAM/primitives/strings/wordRes/wordRes.H
+++ b/src/OpenFOAM/primitives/strings/wordRes/wordRes.H
@@ -86,8 +86,12 @@ public:
 
     // Static Data / Methods
 
-        //- Return a null wordRes - a reference to the NullObject
-        inline static const wordRes& null();
+        //- Return a null wordRes (reference to a nullObject).
+        //- Behaves like a empty wordRes.
+        static const wordRes& null() noexcept
+        {
+            return NullObjectRef<wordRes>();
+        }
 
         //- Return a wordRes with duplicate entries filtered out.
         //  No distinction made between literals and regular expressions.
diff --git a/src/OpenFOAM/primitives/strings/wordRes/wordResI.H b/src/OpenFOAM/primitives/strings/wordRes/wordResI.H
index e82a49c89f..2b72076d96 100644
--- a/src/OpenFOAM/primitives/strings/wordRes/wordResI.H
+++ b/src/OpenFOAM/primitives/strings/wordRes/wordResI.H
@@ -27,12 +27,6 @@ License
 
 // * * * * * * * * * * * * * Static Member Functions * * * * * * * * * * * * //
 
-inline const Foam::wordRes& Foam::wordRes::null()
-{
-    return NullObjectRef<wordRes>();
-}
-
-
 inline Foam::label Foam::wordRes::first_match
 (
     const UList<wordRe>& selectors,
diff --git a/src/fileFormats/ensight/file/ensightFile.H b/src/fileFormats/ensight/file/ensightFile.H
index e565f3eb2c..2e16f0e95d 100644
--- a/src/fileFormats/ensight/file/ensightFile.H
+++ b/src/fileFormats/ensight/file/ensightFile.H
@@ -92,7 +92,7 @@ public:
     // Static Functions
 
         //- Return a null ensightFile
-        static const ensightFile& null()
+        static const ensightFile& null() noexcept
         {
             return NullObjectRef<ensightFile>();
         }
diff --git a/src/fileFormats/ensight/file/ensightGeoFile.H b/src/fileFormats/ensight/file/ensightGeoFile.H
index 86d2d9beed..54c8078a6a 100644
--- a/src/fileFormats/ensight/file/ensightGeoFile.H
+++ b/src/fileFormats/ensight/file/ensightGeoFile.H
@@ -72,7 +72,7 @@ public:
     // Static Functions
 
         //- Return a null ensightGeoFile
-        static const ensightGeoFile& null()
+        static const ensightGeoFile& null() noexcept
         {
             return NullObjectRef<ensightGeoFile>();
         }
diff --git a/src/finiteArea/fields/faPatchFields/basic/sliced/slicedFaPatchField.C b/src/finiteArea/fields/faPatchFields/basic/sliced/slicedFaPatchField.C
index fb9846b148..650beb7daa 100644
--- a/src/finiteArea/fields/faPatchFields/basic/sliced/slicedFaPatchField.C
+++ b/src/finiteArea/fields/faPatchFields/basic/sliced/slicedFaPatchField.C
@@ -127,7 +127,7 @@ template<class Type>
 Foam::slicedFaPatchField<Type>::~slicedFaPatchField()
 {
     // Set to nullptr to avoid deletion of underlying field
-    UList<Type>::shallowCopy(UList<Type>());
+    UList<Type>::shallowCopy(nullptr);
 }
 
 
diff --git a/src/finiteArea/fields/faePatchFields/basic/sliced/slicedFaePatchField.C b/src/finiteArea/fields/faePatchFields/basic/sliced/slicedFaePatchField.C
index fd746a305e..9f0e1818ab 100644
--- a/src/finiteArea/fields/faePatchFields/basic/sliced/slicedFaePatchField.C
+++ b/src/finiteArea/fields/faePatchFields/basic/sliced/slicedFaePatchField.C
@@ -127,7 +127,7 @@ template<class Type>
 Foam::slicedFaePatchField<Type>::~slicedFaePatchField()
 {
     // Set to nullptr to avoid deletion of underlying field
-    UList<Type>::shallowCopy(UList<Type>());
+    UList<Type>::shallowCopy(nullptr);
 }
 
 
diff --git a/src/finiteVolume/fields/fvPatchFields/basic/sliced/slicedFvPatchField.C b/src/finiteVolume/fields/fvPatchFields/basic/sliced/slicedFvPatchField.C
index a15239c2bb..c053c9b934 100644
--- a/src/finiteVolume/fields/fvPatchFields/basic/sliced/slicedFvPatchField.C
+++ b/src/finiteVolume/fields/fvPatchFields/basic/sliced/slicedFvPatchField.C
@@ -127,7 +127,7 @@ template<class Type>
 Foam::slicedFvPatchField<Type>::~slicedFvPatchField()
 {
     // Set to nullptr to avoid deletion of underlying field
-    UList<Type>::shallowCopy(UList<Type>());
+    UList<Type>::shallowCopy(nullptr);
 }
 
 
diff --git a/src/finiteVolume/fields/fvsPatchFields/basic/sliced/slicedFvsPatchField.C b/src/finiteVolume/fields/fvsPatchFields/basic/sliced/slicedFvsPatchField.C
index 08179b72e8..717918883f 100644
--- a/src/finiteVolume/fields/fvsPatchFields/basic/sliced/slicedFvsPatchField.C
+++ b/src/finiteVolume/fields/fvsPatchFields/basic/sliced/slicedFvsPatchField.C
@@ -127,7 +127,7 @@ template<class Type>
 Foam::slicedFvsPatchField<Type>::~slicedFvsPatchField()
 {
     // Set to nullptr to avoid deletion of underlying field
-    UList<Type>::shallowCopy(UList<Type>());
+    UList<Type>::shallowCopy(nullptr);
 }
 
 
diff --git a/src/finiteVolume/finiteVolume/ddtSchemes/ddtScheme/ddtScheme.C b/src/finiteVolume/finiteVolume/ddtSchemes/ddtScheme/ddtScheme.C
index 94a00c2a68..06209c1334 100644
--- a/src/finiteVolume/finiteVolume/ddtSchemes/ddtScheme/ddtScheme.C
+++ b/src/finiteVolume/finiteVolume/ddtSchemes/ddtScheme/ddtScheme.C
@@ -96,11 +96,7 @@ tmp<GeometricField<Type, fvPatchField, volMesh>> ddtScheme<Type>::fvcDdt
 )
 {
     NotImplemented;
-
-    return tmp<GeometricField<Type, fvPatchField, volMesh>>
-    (
-        GeometricField<Type, fvPatchField, volMesh>::null()
-    );
+    return nullptr;
 }
 
 
@@ -113,13 +109,7 @@ tmp<fvMatrix<Type>> ddtScheme<Type>::fvmDdt
 )
 {
     NotImplemented;
-
-    return tmp<fvMatrix<Type>>::New
-    (
-        vf,
-        alpha.dimensions()*rho.dimensions()
-        *vf.dimensions()*dimVol/dimTime
-    );
+    return nullptr;
 }
 
 
@@ -130,15 +120,10 @@ tmp<GeometricField<Type, fvsPatchField, surfaceMesh>> ddtScheme<Type>::fvcDdt
 )
 {
     NotImplemented;
-
-    return tmp<GeometricField<Type, fvsPatchField, surfaceMesh>>
-    (
-        GeometricField<Type, fvsPatchField, surfaceMesh>::null()
-    );
+    return nullptr;
 }
 
 
-
 template<class Type>
 tmp<surfaceScalarField> ddtScheme<Type>::fvcDdtPhiCoeff
 (
diff --git a/src/finiteVolume/fvMatrices/fvMatrix/fvMatrix.C b/src/finiteVolume/fvMatrices/fvMatrix/fvMatrix.C
index 6b15f83645..716a2b1896 100644
--- a/src/finiteVolume/fvMatrices/fvMatrix/fvMatrix.C
+++ b/src/finiteVolume/fvMatrices/fvMatrix/fvMatrix.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2016-2023 OpenCFD Ltd.
+    Copyright (C) 2016-2024 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -894,13 +894,13 @@ void Foam::fvMatrix<Type>::transferFvMatrixCoeffs()
 template<class Type>
 Foam::lduPrimitiveMeshAssembly* Foam::fvMatrix<Type>::lduMeshPtr()
 {
-    const lduPrimitiveMeshAssembly* lduAssemMeshPtr =
-        psi_.mesh().thisDb().objectRegistry::template findObject
+    return
+    (
+        psi_.mesh().thisDb().objectRegistry::template getObjectPtr
         <
             lduPrimitiveMeshAssembly
-        > (lduAssemblyName_);
-
-    return const_cast<lduPrimitiveMeshAssembly*>(lduAssemMeshPtr);
+        > (lduAssemblyName_)
+    );
 }
 
 
diff --git a/src/mesh/blockMesh/PDRblockMesh/PDRblock.C b/src/mesh/blockMesh/PDRblockMesh/PDRblock.C
index 5e27e50075..10db4aeb8a 100644
--- a/src/mesh/blockMesh/PDRblockMesh/PDRblock.C
+++ b/src/mesh/blockMesh/PDRblockMesh/PDRblock.C
@@ -106,12 +106,6 @@ bool Foam::PDRblock::checkMonotonic
 }
 
 
-const Foam::PDRblock& Foam::PDRblock::null()
-{
-    return NullObjectRef<PDRblock>();
-}
-
-
 // * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
 void Foam::PDRblock::addDefaultPatches()
diff --git a/src/mesh/blockMesh/PDRblockMesh/PDRblock.H b/src/mesh/blockMesh/PDRblockMesh/PDRblock.H
index 8df077c4f4..d0302b075b 100644
--- a/src/mesh/blockMesh/PDRblockMesh/PDRblock.H
+++ b/src/mesh/blockMesh/PDRblockMesh/PDRblock.H
@@ -429,8 +429,11 @@ public:
 
     // Static Member Functions
 
-        //- Return a PDRblock reference to a nullObject
-        static const PDRblock& null();
+        //- Return a null PDRblock (reference to a nullObject).
+        static const PDRblock& null() noexcept
+        {
+            return NullObjectRef<PDRblock>();
+        }
 
 
     // Constructors
diff --git a/src/optimisation/adjointOptimisation/adjoint/boundaryAdjointContributions/boundaryAdjointContribution/boundaryAdjointContribution.C b/src/optimisation/adjointOptimisation/adjoint/boundaryAdjointContributions/boundaryAdjointContribution/boundaryAdjointContribution.C
index a8220f2639..a36d646dff 100644
--- a/src/optimisation/adjointOptimisation/adjoint/boundaryAdjointContributions/boundaryAdjointContribution/boundaryAdjointContribution.C
+++ b/src/optimisation/adjointOptimisation/adjoint/boundaryAdjointContributions/boundaryAdjointContribution/boundaryAdjointContribution.C
@@ -144,7 +144,7 @@ tmp<fvPatchScalarField>
 boundaryAdjointContribution::turbulentDiffusivity() const
 {
     NotImplemented;
-    return tmp<fvPatchScalarField>(nullptr);
+    return nullptr;
 }
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
diff --git a/src/overset/lduPrimitiveProcessorInterface/GAMG/calculatedProcessorGAMGInterfaceField.H b/src/overset/lduPrimitiveProcessorInterface/GAMG/calculatedProcessorGAMGInterfaceField.H
index d1e78eed35..f06a90edb8 100644
--- a/src/overset/lduPrimitiveProcessorInterface/GAMG/calculatedProcessorGAMGInterfaceField.H
+++ b/src/overset/lduPrimitiveProcessorInterface/GAMG/calculatedProcessorGAMGInterfaceField.H
@@ -133,7 +133,7 @@ public:
         ) const
         {
             NotImplemented;
-            return autoPtr<GAMGInterfaceField>(nullptr);
+            return nullptr;
         }
 
 
diff --git a/src/overset/oversetCoupledPolyPatch/oversetGAMGInterfaceField/oversetGAMGInterfaceField.H b/src/overset/oversetCoupledPolyPatch/oversetGAMGInterfaceField/oversetGAMGInterfaceField.H
index 5edbd651f6..640a9940a2 100644
--- a/src/overset/oversetCoupledPolyPatch/oversetGAMGInterfaceField/oversetGAMGInterfaceField.H
+++ b/src/overset/oversetCoupledPolyPatch/oversetGAMGInterfaceField/oversetGAMGInterfaceField.H
@@ -105,7 +105,7 @@ public:
         ) const
         {
             NotImplemented;
-            return autoPtr<GAMGInterfaceField>(nullptr);
+            return nullptr;
         }
 
 
diff --git a/src/phaseSystemModels/multiphaseInter/phasesSystem/multiphaseInterSystem/multiphaseInterSystem.H b/src/phaseSystemModels/multiphaseInter/phasesSystem/multiphaseInterSystem/multiphaseInterSystem.H
index fbcacaefbc..b9dfffb4a4 100644
--- a/src/phaseSystemModels/multiphaseInter/phasesSystem/multiphaseInterSystem/multiphaseInterSystem.H
+++ b/src/phaseSystemModels/multiphaseInter/phasesSystem/multiphaseInterSystem/multiphaseInterSystem.H
@@ -367,7 +367,7 @@ public:
         ) const
         {
             NotImplemented;
-            return tmp<scalarField>::New(p);
+            return nullptr;
         }
 
         //- Return Cv of the mixture
diff --git a/src/phaseSystemModels/reactingEuler/multiphaseSystem/phaseModel/PurePhaseModel/PurePhaseModel.C b/src/phaseSystemModels/reactingEuler/multiphaseSystem/phaseModel/PurePhaseModel/PurePhaseModel.C
index 6279a080a4..de620d523a 100644
--- a/src/phaseSystemModels/reactingEuler/multiphaseSystem/phaseModel/PurePhaseModel/PurePhaseModel.C
+++ b/src/phaseSystemModels/reactingEuler/multiphaseSystem/phaseModel/PurePhaseModel/PurePhaseModel.C
@@ -88,7 +88,7 @@ Foam::PurePhaseModel<BasePhaseModel>::Y(const word& name) const
         << "Cannot get a species fraction by name from a pure phase"
         << exit(FatalError);
 
-    return NullObjectRef<volScalarField>();
+    return volScalarField::null();
 }
 
 
diff --git a/src/thermophysicalModels/solidChemistryModel/basicSolidChemistryModel/basicSolidChemistryModel.C b/src/thermophysicalModels/solidChemistryModel/basicSolidChemistryModel/basicSolidChemistryModel.C
index 5076b34ca8..2653f238ce 100644
--- a/src/thermophysicalModels/solidChemistryModel/basicSolidChemistryModel/basicSolidChemistryModel.C
+++ b/src/thermophysicalModels/solidChemistryModel/basicSolidChemistryModel/basicSolidChemistryModel.C
@@ -59,7 +59,7 @@ const Foam::DimensionedField<Foam::scalar, Foam::volMesh>&
 Foam::basicSolidChemistryModel::RR(const label i) const
 {
     NotImplemented;
-    return (volScalarField::Internal::null());
+    return volScalarField::Internal::null();
 }
 
 
@@ -67,14 +67,11 @@ Foam::DimensionedField<Foam::scalar, Foam::volMesh>&
 Foam::basicSolidChemistryModel::RR(const label i)
 {
     NotImplemented;
-
-    return dynamic_cast<volScalarField::Internal&>
-    (
+    return
         const_cast<volScalarField::Internal&>
         (
             volScalarField::Internal::null()
-        )
-    );
+        );
 }
 
 
@@ -86,14 +83,7 @@ Foam::basicSolidChemistryModel::calculateRR
 ) const
 {
     NotImplemented;
-
-    return dynamic_cast<tmp<volScalarField::Internal>&>
-    (
-        const_cast<volScalarField::Internal&>
-        (
-            volScalarField::Internal::null()
-        )
-    );
+    return nullptr;
 }
 
 
diff --git a/src/thermophysicalModels/specie/reaction/Reactions/Reaction/Reaction.C b/src/thermophysicalModels/specie/reaction/Reactions/Reaction/Reaction.C
index 89b9fa51e2..ad096ee103 100644
--- a/src/thermophysicalModels/specie/reaction/Reactions/Reaction/Reaction.C
+++ b/src/thermophysicalModels/specie/reaction/Reactions/Reaction/Reaction.C
@@ -441,7 +441,7 @@ const Foam::List<typename Foam::Reaction<ReactionThermo>::specieCoeffs>&
 Foam::Reaction<ReactionThermo>::glhs() const
 {
     NotImplemented;
-    return NullObjectRef<List<specieCoeffs>>();
+    return List<specieCoeffs>::null();
 }
 
 
@@ -450,7 +450,7 @@ const Foam::List<typename Foam::Reaction<ReactionThermo>::specieCoeffs>&
 Foam::Reaction<ReactionThermo>::grhs() const
 {
     NotImplemented;
-    return NullObjectRef<List<specieCoeffs>>();
+    return List<specieCoeffs>::null();
 }