code: private V putForNullKey(V value) {
  	for (Entry<K, V> e = table[0]; e != null; e = e.next) {
  	    if (e.key == null) {
  		V oldValue = e.value;
  		e.value = value;
  		e.recordAccess(this);
  		return oldValue;
  	    }
  	}
  	modCount++;
  	addEntry(0, null, value, 0);
  	return null;
      }
docs: Offloaded version of put for null keys