`To begin with,' said the Cat, `a dog's not mad.  You grant
that?'

  `I suppose so,' said Alice.

  `Well, then,' the Cat went on, `you see, a dog growls when it's
angry, and wags its tail when it's pleased.  Now I growl when I'm
pleased, and wag my tail when I'm angry.  Therefore I'm mad.'

  `I call it purring, not growling,' said Alice.

        @SuppressWarnings("unchecked") // unsafe, but Javadoc warns about it
        K k = (K) key;
        return function.apply(k);
      } else {
        return null;
      }
    }

    @Override
    @CheckForNull
    public V remove(@CheckForNull Object key) {
      if (backingSet().remove(key)) {
        @SuppressWarnings("unchecked") // unsafe, but Javadoc warns about it
        K k = (K) key;

  `To begin with,' said the Cat, `a dog's not mad.  You grant
that?'

  `I suppose so,' said Alice.

  `Well, then,' the Cat went on, `you see, a dog growls when it's
angry, and wags its tail when it's pleased.  Now I growl when I'm
pleased, and wag my tail when I'm angry.  Therefore I'm mad.'

  `I call it purring, not growling,' said Alice.