code: public MapBuilder<KEY, VALUE> put(KEY key, VALUE value) {
      getMap().put(key, value);
      return this;
    }
docs: Puts the given {@link KEY key} and {@link VALUE value} into the {@link Map} being built
  by this {@link MapBuilder builder}.
  
  @param key {@link KEY key} to put.
  @param value {@link VALUE value} to put mapped to the given {@link KEY key}.
  @return this {@link MapBuilder}.
  @see java.util.Map#put(Object, Object)