mysql - Insert in nullable FK -

mysql - Insert in nullable FK -

i have table x has fields , 1 of them fk representing id of table y, fk not need filled, set nullable, when i'm going insert in laravel or phpmyadmin test, next message returned # 1452 - can not add together or update kid row: foreign key constraint fails

i wonder how can insert allowing me leave null fk.

mysql laravel