code: @Override
      public <T> VertexProperty<T> property(String key) {
          T value = value(key);
          if (value == null) {
              return VertexProperty.<T>empty();
          } else {
              return new BitsyVertexProperty<T>(this, key, value);
          }
      }
docs: THERE ARE TWO MORE COPIES OF THIS CODE IN ELEMENT AND EDGE