Sahil,
The ORA-01451 error seems to be related to the column being modified to NULL cannot be modified to NULL. I found an article that shows each ORA error, and if you search the error there are some Causes and Actions you might be able to take to remedy the issue.
https://docs.oracle.com/cd/A58617_01/server.804/a58312/newch223.htm. I have also wrote it below:
"Cause: The column may already allow NULL values, the NOT NULL constraint is part of a primary key or check constraint, or an ALTER TABLE MODIFY statement attempted to change a column specification unnecessarily, from NULL to NULL.
Action: If a primary key or check constraint is enforcing the NOT NULL constraint, then drop that constraint."
Without knowing the attribute and how it was created makes knowing the specific issue harder.
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Allan Henle
Projetech Inc.
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