laravel 5.1 ErrorException: preg_replace(): Parameter mismatch, pattern is a string while replacement is an array

I have the following model with fillable properties:

class Job extends Model {

    protected $fillable = [
      'job_type_id',
      'user_id',
      'start_at',
      'end_at',
      'job_title',
      'job_ref',
      'job_desc'

    ];

    // other stuff
 }

I have a form to update the job which includes some multiselect dropdown lists as follows:

<div class="form-group ">
    <label for="job_title">Job title</label>
    <input id="job_title" class="form-control" type="text" name="job_title">
</div>

<div class="form-group ">
   <label for="industry_list">Industry</label>
   <select id="industry_list" class="form-control name="industry_list[]" multiple="" >
     <option value="1">Accounting</option>
     <option value="37">Administration</option>
     ...
   </select>
</div>

In my controller I have the following method to update the job but I get error:

ErrorException in helpers.php line 671: preg_replace(): Parameter mismatch, pattern is a string while replacement is an array

It seems like using Auth::user()->jobs()->update($request->except('job_type_id')); is causing this error because the request object contains an array for the industry_list. But why should this matter as I've defined the mass fillable attributes on the Job class?

public function update(JobRequest $request, $id)
{
   $job = Job::findOrFail($id);

   Auth::user()->jobs()->update($request->except('job_type_id'));

   $job->industries()->sync($request->input('industry_list'));

   flash()->success('Job details have been updated');

   return redirect('/job/' . $id . '/edit');

}

via Chebli Mohamed