unexpected NULL passed to SIGNAL routine

  Explanation:  The value  expression  which  was  passed  to  the
  SIGNAL routine was NULL.  This is not permitted.

  User Action:  Correct the application so that NULL is not passed
  to  the SIGNAL routine.  For instance use COALESCE (:mysqlstate,
  '22023').  SQL92 defines 22023  as  "data  exception  -  invalid
  parameter value".