So far, the "wrong-type-argument stringp nil" error no longer comes back, it seems your fix works. Thanks a lot.
However, I'm now getting the "No references found" message whenever I use "semantic-symref-symbol" trying to get all the references to any symbol, whether the symbol is a C++ class member variable or a local variable, it just couldn't find any reference. The gtag database are under my project root. In my .emacs file I have the following:
When I type "Global -xs symbol" under command line, it shows all the reference to the symbol correctly. But why semantic couldn't find anything? On the other hand, 'semantic-symref' works fine on looking for references of a class or class member function, but it doesn't work for variables.
Is it simply another bug, or am I missing anything that keeps symbol reference from working?