Quoting Clang:
"reference cannot be bound to dereferenced null pointer in well-defined
C++ code; comparison may be assumed to always evaluate to false"
Conflicts:
Sources/CMakeLists.txt
Also changed all "if (this==NULL) return;"s.
Fixes some -Wtautological-undefined-compare warnings.
Quoting Clang:
"'this' pointer cannot be null in well-defined C++ code; comparison may
be assumed to always evaluate to false"
