mpris implementation issues

[kotontrion]

From the dbus specification:

If org.freedesktop.DBus.Properties.GetAll is called with a valid interface name which contains no properties, an empty array should be returned. If it is called with a valid interface name for which some properties are not accessible to the caller, those properties should be silently omitted from the result array. If org.freedesktop.DBus.Properties.Get is called for any such properties, an appropriate access control error should be returned.

So in this project here, some properties of the mpris interface are not implemented, like eg, Position, SupportedUriSchemes and SupportedMimeTypes. Yet when calling org.freedesktop.DBus.Properties.Get for those properties, blanket will return false, but according to the dbus specification it should return an error.

We came across this issue with the mpris library from this project. Valas dbus proxy will try to get those properties and will crash when trying to unpack the variant, as the types do not match. When an error is returned instead of falseeverything works as expected.