code: public <N extends Number & Comparable<?>> NumberExpression<T> add(Expression<N> right) {
          return Expressions.numberOperation(getType(), Ops.ADD, mixin, right);
      }
docs: Create a {@code this + right} expression
  
  <p>Returns the sum of this and right</p>
  
  @param right rhs of expression
  @return this + right