PVS-Studio warning V595 for Newton Game Dynamics

void dgRedBackNode::RotateLeft(dgRedBackNode** const head)
{
  ....
  me->m_right = child->m_left;
  ....
  if (child != NULL) {
    child->m_parent = me->m_parent;
  }
  ....
}

This suspicious code was found in Newton Game Dynamics project by PVS-Studio static code analyzer.
Warning message is:
V595 The 'child' pointer was utilized before it was verified against nullptr. Check lines: 78, 84. dgtree.cpp 78

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