code: private boolean valueEquals(V leftValue, V rightValue) {
          if (leftValue == rightValue) {
              return true;
          }
          if (leftValue == null || rightValue == null) {
              return false;
          }
          return leftValue.equals(rightValue);
      }
docs: Value equals.
  
  @param leftValue
  the left value
  @param rightValue
  the right value
  @return the boolean