515: Cannot insert the value NULL into column

What does it mean?

An attempt was made to insert or update a NULL value into a column defined as NOT NULL. The operation was rejected because the column does not allow nulls.

Why does it happen?

A required column omitted from the INSERT statement, missing/empty fields in the source data, a NOT NULL column without a default value, or NULL sent by the application.

How to fix it

Supply a valid value for required columns. Add DEFAULT constraints to appropriate columns. Validate the source data for missing fields and assign defaults with ISNULL/COALESCE. If the column does not really need to be mandatory, review the schema to allow NULL.