how set GUC_check_errhint_string in call_string_check_hook()

Dear all,

I need help to send hint message to erreport()  in  call_string_check_hook function [src/backend/utils/misc/guc.c:8092]

In   call_string_check_hook(), following parameter are resets

  /* Reset variables that might be set by hook */
8100         GUC_check_errcode_value = ERRCODE_INVALID_PARAMETER_VALUE;
8101         GUC_check_errmsg_string = NULL;
8102         GUC_check_errdetail_string = NULL;
8103         GUC_check_errhint_string = NULL;

at line 8107 in ereport() it has conditional operation as

8113GUC_check_errdetail_string ?

8114                                  errdetail_internal("%s", GUC_check_errdetail_string) : 0,

I have basic questions,
 
1. Condition testing of  GUC_check_errdetail_string or other GUC_*  is needed, even if we resting it?
2. Can I pass hint message in above ereport(), how?

Thanks in advance !

Regards,
Amul Sul