Trying to access array offset on value of type null in encrypt_config_form()

On the "Add configuration" form, there is not a third parameter passed to encrypt_config_form(), i.e. $config parameter is NULL. Further down in that form constructor are multiple references to $config['method'].

When running on PHP 7.4, this causes the following notices to appear in the logs or on the screen:

Notice: Trying to access array offset on value of type null in encrypt_config_form() (line 131 of ..snip../encrypt/includes/encrypt.admin.inc).

I'm attaching a patch I wrote to wrap these in isset(). Hope this is useful for other folks migrating to PHP 7.4.