PVS-Studio warning V501 for libxml

static int
xmlSchemaCheckCOSNSSubset(....)
{
  ...
  if ((sub->negNsSet != NULL) &&
      (super->negNsSet != NULL) &&
      (sub->negNsSet->value == sub->negNsSet->value))
   return 0;
 ...
}

This is what should have been written here: (sub->negNsSet->value == super->negNsSet->value))

This suspicious code was found in libxml project by PVS-Studio static code analyzer.
Warning message is:
V501 There are identical sub-expressions 'sub->negNsSet->value' to the left and to the right of the '==' operator. libxml xmlschemas.c 13949

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