create or replace procedure zz is begin null; end zz;
/
drop procedure zz;
col owner format a30
col object_name format a30
select o.OWNER,o.OBJECT_NAME from dba_objects_ae o
 where o.OBJECT_TYPE = 'NON-EXISTENT' and o.OWNER = user and o.OBJECT_NAME = 'ZZ';
exec dbms_scheduler.create_job(job_name =>'ZZ',job_type =>'PLSQL_BLOCK',job_action => 'begin null; end;');

Procedure created.

SQL>
Procedure dropped.

SQL> SQL> SQL>   2
OWNER                          OBJECT_NAME
------------------------------ ------------------------------
SYS                            ZZ

SQL> BEGIN dbms_scheduler.create_job(job_name =>'ZZ',job_type =>'PLSQL_BLOCK',job_action => 'begin null; end;'); END;

*
ERROR at line 1:
ORA-27477: "SYS"."ZZ" already exists
ORA-06512: at "SYS.DBMS_ISCHED", line 146
ORA-06512: at "SYS.DBMS_SCHEDULER", line 288
ORA-06512: at line 1