code: @SuppressWarnings("unchecked")
      @Override
      protected Val<Expression> arg(String field, String op, Val<Expression> arg,
                                    int index, int count, QueryExprMeta parent) {
          Iterable<ExprArgTransformer> transformers = getTransformer(ExprArgTransformer.class);
          for (ExprArgTransformer transformer : transformers) {
              Transformed<Val<Expression>> transformed = transformer.transform(
                      field, op, arg, index, count, this, parent
              );
              if (transformed.success()) {
                  return transformed.result();
              }
          }
          throw new QuerySyntaxException(Messages.get("dsl.transform.err", field, op, String.valueOf(arg)));
      }
docs: {@inheritDoc}