Nice and quick: add @ symbol before $args on line 506
Not a good fix as the error is an indication of an underlying problem, i.e. the post ID not being passed and it therefore not being a valid request for authorization.
Better would be to add an isset( $args ) at the start of the if() clause as if it's not set the return value should not be changed.
isset( $args )
Absolutely. I hadn't thought it through.
Fix issue #492
Closing in favour of pull request #499 which solves this.