What does NULL in V$SQL(MODULE) mean?

Greeting All.

Hope this is a simple question. I am using Oracle 11.2.0.2. When I try to collect some application SQL for analysys but filter out SQL statements fired from SQL*Plus or Toad by using column module in V$SQL or V$SQLAREA, I realized many rows having NULL values in MODULE column. I know no one uses DBMS_APPLICATION_INFO to set MODULE explicitly. So what does NULL imply here?