How to Validate an array in Laravel

From the Laravel documentation:

Validating array based form input fields doesn't have to be a pain. You may use "dot notation" to validate attributes within an array. For example, if the incoming HTTP request contains a photos[profile] field, you may validate it like so:

use Illuminate\Support\Facades\Validator;

$validator = Validator::make($request->all(), [
    'photos.profile' => 'required|image',
]);

You may also validate each element of an array. For example, to validate that each email in a given array input field is unique, you may do the following:

$validator = Validator::make($request->all(), [
    'person.*.email' => 'email|unique:users',
    'person.*.first_name' => 'required_with:person.*.last_name',
]);

In your case, if you want to validate that the elements inside your array are not empty, the following would suffice:

'topics' => 'required|array',
'topics.*' => 'sometimes|integer', // <- for example.