Error on new installation: Argument #1 ($array) must be of type array, null given in array_keys()

Problem/Motivation

Steps to reproduce

1. Install a fresh Drupal instance.
2. Enable the field_permissions module.
3. Try to change configuration of any field

Proposed resolution

Update the getPermissions() method to ensure $permissions is always an array before calling array_keys(), e.g.:

$permissions = $permissions ?? [];