code: public Range<T> extend(T value) {
          if (value == null)
              throw new IllegalArgumentException("value must not be null");
          return extend(value, value);
      }
docs: Returns the smallest range that includes this range and
  the {@code value}.
  <p>
  See {@link #extend(Range)} for more details, as this method is
  equivalent to {@code extend(Range.create(value, value))}.</p>
  
  @param value a non-{@code null} {@code T} reference
  @return the extension of this range and the value.
  @throws NullPointerException if {@code value} was {@code null}