code: public Filter add(String attribute, Operator op, Object value) {
          return add(new Predicate(attribute, op, value));
      }
docs: Adds the given Predicate to the list of predicates.
  
  @param attribute the attribute
  @param op the operator
  @param value the value
  @return this for chaining.
  @see Predicate(String, Operator, Object)