code: public boolean contains(final T element) {
          if (element == null) {
              return false;
          }
  
          return lowerEndpoint.includes(element) && upperEndpoint.includes(element);
      }
docs: <p>
  Checks whether the specified element occurs within this range.
  </p>
  
  @param element
  the element to check for, null returns false
  @return true if the specified element occurs within this range