regexp-instr() function works fine...

Code:
SQL> 
SQL> select regexp_instr('trina_7777777777','[A-Z]') from dual;

REGEXP_INSTR('TRINA_7777777777','[A-Z]')
---------------------------------------------------------------
                                                              0

SQL> 
SQL> select regexp_instr('trina_B777777777','[A-Z]') from dual;

REGEXP_INSTR('TRINA_B777777777','[A-Z]')
---------------------------------------------------------------
                                                              7

SQL>
Why are you not raising application error anymore?