Reverted change concerning the location of the construction of the "null" strings.

Changed dotFoam function to use null-constructed strings rather that the "null" strings.

src/OpenFOAM/primitives/strings/string/string.C

@@ -32,6 +32,7 @@ License
 
 const char* const Foam::string::typeName = "string";
 int Foam::string::debug(debug::debugSwitch(string::typeName, 0));
+const Foam::string Foam::string::null;
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //