PVS-Studio warning V595 for Firefox

void
nsHttpTransaction::RestartVerifier::Set(int64_t contentLength,
                                        nsHttpResponseHead *head)
{
  if (mSetup)
    return;

  if (head->Status() != 200)
    return;

  mContentLength = contentLength;

  if (head) {
  ....
}

This suspicious code was found in Firefox project by PVS-Studio static code analyzer.
Warning message is:
V595 The 'head' pointer was utilized before it was verified against nullptr. Check lines: 1915, 1920. nshttptransaction.cpp 1915

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