PVS-Studio warning V595 for FlightGear

static int tokMatch(struct Token* a, struct Token* b)
{
  int i, l = a->strlen;
  if(!a || !b) return 0;
  ....
}

This suspicious code was found in FlightGear project by PVS-Studio static code analyzer.
Warning message is:
V595 The 'a' pointer was utilized before it was verified against nullptr. Check lines: 478, 479. codegen.c 478

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/