docs: public Set<K> keySet()
    {
      if (TraceComponent.isAnyTracingEnabled() && _tc.isEntryEnabled()) SibTr.entry(this, _tc, "keySet");
      
      UnsupportedOperationException uoe = new UnsupportedOperationException();
      
      if (TraceComponent.isAnyTracingEnabled() && _tc.isEntryEnabled()) SibTr.exit(this, _tc, "keySet", uoe);
      throw uoe;
    }