Oracle Database Discussions

I have query to get hash value password.  It works in 11g.  But in 12c, some users are retrieving blanks.

this is the query:

select  extract(xmltype(dbms_metadata.get_xml('USER',username)),'//USER_T/PASSWORD/text()').getStringVal()

from dba_users;

some users are ok.  But some users like these are getting empty passwords:

ANONYMOUS

APEX_040200

C##DBFS_ADM1

GSMADMIN_INTERNAL

ORACLE_OCM

...

more

Do I need to user another query for 12c database?

thanks