Answers for "laravel foreignid is null"

foreign key nullable in laravel

$table
      ->foreignId('other_table_id')
      ->nullable() // here
      ->references('id')
      ->on('other_table');

foreignId in laravel

// for laravel 7 or above. 
$table->foreignId('user_id')->constrained();
/*-----------OR---------------*/
$table->foreignId('user_id')->constrained('users');