How to resolve problem about many to many relation with 'sync' function in laravel 5.

syncAlwaysNull.php

<?php

//Problem 1 : Argument 1 passed to Illuminate\Database\Eloquent\Relations\BelongsToMany::formatSyncList() must be of the type array, null given, called
$tabelA->tabelB()->sync($request->get('col1'), $request->get('col2'));

//Problem 2 :  Integrity constraint violation: 1048 Column 'col2_id' cannot be null
$tabelA->tabelB()->sync([$request->get('col1'), $request->get('col2')]);

//How to resolve
$data = array_slice($request->all(), 1); //remove _token post data
$table->tableB()->sync([$data]);