Description
The tool attempted to write a null value to a field that does not support nulls.
Solution
If you're using a tool such as Calculate Field to write field values, modify the calculation to use a different value instead of a null. For example, if the field is of text type, use an empty string ("").
If the tool is writing to an existing field that you can specify, use a different field that supports nulls.
If the table does not have any existing records, use the Alter Field tool to modify the field properties to support nulls.