code: public static void isPositive(Integer value, String name) {
      notNull(value, name);
  
      if (value < 0) {
        throw new IllegalArgumentException(name + "must be a positive number.");
      }
    }
docs: Checks that i is not null and is a positive number
  
  @param value    The integer value to check.
  @param name The name of the variable being checked, included when an error is raised.
  @throws IllegalArgumentException If i is null or less than 0