The Integration Service handles rows with null values in lookup condition columns differently, based on whether the row exists in the cache.
If the row does not exist in the lookup cache, the Integration Service inserts the row into the cache and passes it to the target table. If the row exists in the lookup cache, the Integration Service does not update the row in the cache or target table.
If the source data contains null values in the lookup condition columns, set the error threshold to one. This ensures that the lookup cache and table remain synchronized if the Integration Service inserts a row in the cache, but the database rejects the row due to a Not Null constraint.