assign pointers to NULL after deletion

src/lagrangian/intermediate/particleForces/particleForces.C

@@ -127,6 +127,7 @@ void Foam::particleForces::cacheFields(const bool store)
         if (gradUPtr_)
         {
             delete gradUPtr_;
+            gradUPtr_ = NULL;
         }
     }
 }

src/lagrangian/intermediate/submodels/Kinematic/DispersionModel/DispersionRASModel/DispersionRASModel.C

@@ -95,11 +95,13 @@ void Foam::DispersionRASModel<CloudType>::cacheFields(const bool store)
         if (ownK_ && kPtr_)
         {
             delete kPtr_;
+            kPtr_ = NULL;
             ownK_ = false;
         }
         if (ownEpsilon_ && epsilonPtr_)
         {
             delete epsilonPtr_;
+            epsilonPtr_ = NULL;
             ownEpsilon_ = false;
         }
     }

src/lagrangian/intermediate/submodels/Kinematic/DispersionModel/GradientDispersionRAS/GradientDispersionRAS.C

@@ -72,6 +72,7 @@ void Foam::GradientDispersionRAS<CloudType>::cacheFields(const bool store)
         if (gradkPtr_)
         {
             delete gradkPtr_;
+            gradkPtr_ = NULL;
         }
     }
 }