code: @Override
      public boolean contains(long value, T element) {
      	if (root == null) return false;
      	if (value < first.value) return false;
      	if (value > last.value) return false;
      	if (value == first.value && ObjectUtil.equalsOrNull(element, first.element)) return true;
      	if (value == last.value && ObjectUtil.equalsOrNull(element, last.element)) return true;
      	return contains(root, value, element);
      }
docs: Returns true if the given key exists in the tree and its associated value is the given element.
  Comparison of the element is using the equals method.