code: public static PredicateExpression nin(Object... rhs) {
          PredicateExpression ex = new PredicateExpression("$nin", rhs);
          if (rhs.length == 1) {
              ex.single = true;
          }
          return ex;
      }
docs: The document field must not exist in the list provided
  @param rhs The argument - one or more values
  @return PredicateExpression: $nin rhs