The Oracle Doc explain:
ORA-01405 fetched column value is NULL
Cause: The INTO clause of a FETCH operation contained a NULL value, and
no indicator was used. The column buffer in the program remained unchanged,
and the cursor return code was +2. This is an error unless you are running
Oracle with DBMS=6, emulating version 6, in which case it is only a warning.
Action: You may do any of the following:
1. Use the NVL function to convert the retrieved NULL to another value, such
as zero or blank. This is the simplest solution.
2. Use an indicator to record the presence of the NULL. You probably should
use this option when you want a specific action to be taken when a NULL
3. Revise the cursor definition so that no columns possibly containing NULL
values are retrieved.