PVS-Studio warning V547 for MongoDB

inline const char * after(const char *s, char x);
inline string after(const string& s, char x);
inline const char * after(const char *s, const char *x);
inline string after(string s, string x);

inline const char * after(const char *s, char x) {
  const char *p = strchr(s, x);
  return (p != 0) ? p+1 : "";
}

int main() {
{
  ...
  assert( str::after("abcde", 'x') == "" );
  ...
}

This suspicious code was found in MongoDB project by PVS-Studio static code analyzer.
Warning message is:
V547 Expression 'str::after("abcde", 'x') == ""' is always false. To compare strings you should use strcmp() function. test.cpp 43

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/