Compiler warnings in ConTagModel

[felixsh]

Building ConTagModel from the contag-problem produces compiler warnings. The partial output being:

src/problems/conttag/ContTagModel.hpp:288:22: warning: the compiler can assume that the
address of ‘baseAction’ will never be NULL [-Waddress]
  assert(&baseAction != nullptr);
         ~~~~~~~~~~~~^~~~

The warning comes from this line: assert(&baseAction != nullptr);. It is part of some function which takes baseAction as argument by reference. As far as I know references in C++ can never point to NULL. So the assert line can safely be omitted, which fixes the compiler warnings as well.

Some discussion about it:

• https://stackoverflow.com/questions/2099882/checking-for-a-null-object-in-c
• https://stackoverflow.com/questions/6421083/reference-pointing-to-a-null-object