code: public static Expression mod(String lhs, Long divisor, Long remainder) {
          return new Expression(lhs, "$mod", divisor, remainder);
      }
docs: Divisor and Remainder are both positive or negative integers. Non-integer values result in a
  404 status. Matches documents where the expression (field % Divisor == Remainder) is true,
  and only when the document field is an integer
  @param lhs The field to check
  @param divisor The divisor argument of the mod operation
  @param remainder The remainder argument of the mod operation
  @return Expression: lhs $mod divisor remainder