PVS-Studio warning V547 for samba

static bool samu_correct(struct samu *s1, struct samu *s2)
{
  ....
  if (d2_buf == NULL && d2_buf != NULL) {
    DEBUG(0, ("Logon hours is not set\n"));
    ret = False;
  }
  ....
}

This suspicious code was found in samba project by PVS-Studio static code analyzer.
Warning message is:
V547 Expression is always false. Consider reviewing this expression. pdbtest.c 170

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/