ENH: more consistent use of good() or direct testing instead valid()

src/functionObjects/field/extractEulerianParticles/extractEulerianParticles/extractEulerianParticles.C

@@ -453,7 +453,7 @@ Foam::functionObjects::extractEulerianParticles::extractEulerianParticles
     fvMeshFunctionObject(name, runTime, dict),
     writeFile(runTime, name),
     cloud_(mesh_, "eulerianParticleCloud"),
-    faceZoneName_(word::null),
+    faceZoneName_(),
     zoneID_(-1),
     patchIDs_(),
     patchFaceIDs_(),

src/functionObjects/field/histogram/histogramModels/histogramModel/histogramModel.C

@@ -126,7 +126,7 @@ Foam::histogramModel::histogramModel
 :
     writeFile(mesh, name, "histogram", dict),
     mesh_(mesh),
-    fieldName_(word::null)
+    fieldName_()
 {}
 
 

src/functionObjects/field/norm/norm.C

@@ -88,7 +88,7 @@ Foam::functionObjects::norm::norm
     fieldExpression(name, runTime, dict),
     norm_(normType::L1),
     divisorPtr_(nullptr),
-    divisorFieldName_(word::null),
+    divisorFieldName_(),
     p_(-1)
 {
     read(dict);
@@ -127,7 +127,7 @@ bool Foam::functionObjects::norm::read(const dictionary& dict)
     {
         divisorFieldName_ = dict.get<word>("divisorField");
 
-        if (divisorFieldName_ == word::null)
+        if (divisorFieldName_.empty())
         {
             FatalIOErrorInFunction(dict)
                 << "The norm 'field' needs the input entry 'divisorField'."

src/functionObjects/field/resolutionIndex/resolutionIndexModels/resolutionIndexModel/resolutionIndexModel.C

@@ -78,7 +78,7 @@ Foam::resolutionIndexModel::resolutionIndexModel
 )
 :
     mesh_(mesh),
-    resultName_(word::null)
+    resultName_()
 {}