how to return all join table including null foreign key values

I want to join two tables yet it will only return the not nulled foreign key column

it will all only show if i use 1 as default value to all and put nothing inside the foreign id 1 row to look like its empty but the problem there is if i update one row that has default 1 value it will update all foreign id with 1 value and i don't want that to happen.

$unit = DB::table('franchises')
       ->join('units', 'franchises.id', '=', 'units.franchise_id')
       ->orderBy('units.created_at', 'desc')->paginate(20);

return view('register-unit', compact('unit'));

i have this migration query

$table->integer('franchise_id')->unsigned()->default(null); 
$table->foreign('franchise_id')->references('id')->on('franchises')->onDelete('cascade')->onUpdate('cascade');

i want it to make the all foreign key null as a default and still can return all using join. How can i attain it?

via Chebli Mohamed