How to fix Laravel Old value htmlspecialchars() expects parameter 1 to be string, array given?

The "select" element is multiple select element. I am trying to get the old values and select the options selected during the form submissions.

 <select class="form-control w-50" name="keywords[]" id="keywords" multiple="multiple">
 </select>

I am using Select2 for this element. Data is populated from remote source.

In blade

raises the error message that says "htmlspecialchars() expects parameter 1 to be string, array given".

What could be the problem?

via Chebli Mohamed