Audit enabled and no SQL Text is recorded

Hi I enabled Audit and looks start auditing .  I did following steps after enabled in DB level

AUDIT select,alter,INSERT, DELETE, UPDATE ON  <Schema>.<table> BY ACCESS WHENEVER SUCCESSFUL;

select  os_username, username,userhost,terminal,obj_name,action_name,timestamp,SQL_TEXT   from  dba_audit_trail.

can find records are start auditing. But not able to find executed SQL. This SQL_TEXT has null.  How to audit command executed. I referred 1299033.1 doc

Any one can help me would be greatly appreciated.

Thanks