Golang mariadb select does not return signal error

i created a function in MariaDB which its body is:

BEGIN
  SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'MY_ERROR_MESSAGE';
  RETURN 1;
END

Then in Golang, I tried to select this function, which must be done with an error.

dbResult := db.QueryRow("SELECT `function1`()")
    if dbResult.Err() != nil {
        fmt.Printf("error (%s)", dbResult.Err().Error())
    }

but the problem is that Err() is nil !!!!!!!!!! What is the problem !? and fmt.Printf is not executed.

The funny part is that i created a procedure this time

BEGIN
      SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'MY_ERROR_MESSAGE';
END

and i used the same golang code to call it

dbResult := db.QueryRow("CALL `procedure1`()")
        if dbResult.Err() != nil {
            fmt.Printf("error (%s)", dbResult.Err().Error())
        }

but this time everything is OK !!! and .Err is not nil any more ! Why ???? What is the problem