I try submitting data on my sub-category and showing me this error. How do i solve it?

This is the error: Illuminate \ Database \ QueryException (23000) SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'category_id' cannot be null (SQL: insert into subs (category_id, name, updated_at, created_at) values (, Apple Casing, 2017-12-06 00:44:31, 2017-12-06 00:44:31))