@CheckForNull
    public V2 get(@CheckForNull Object key) {
      V1 value = fromMap.get(key);
      if (value != null || fromMap.containsKey(key)) {
        // The cast is safe because of the containsKey check.
        return transformer.transformEntry((K) key, uncheckedCastNullableTToT(value));
      }
      return null;
    }

    // safe as long as the user followed the <b>Warning</b> in the javadoc