Oracle Message QSM-02020 - container column not in SELECT list with NOT NULL constraint

ERRORcontainer column not in SELECT list with NOT NULL constraint
CAUSEThe capability in question is not supported when the materialized views container table has a column that does not correspond to an output expression in the select list, and that column has a NOT NULL constraint. This situation can result in problems during refresh since any new rows inserted into the materialized view will set that column to NULL.
ACTIONDisable or remove the NOT NULL constraint.