[feature request] Overload basic methods to allow nullable returns

[robbiemu]

I like this library :) great little convenience lib.

instead of having to write stuff like Prefs.getLong(myKey, null); — let us write: Prefs.getLong(myKey); // warning: nullable

[abdulrehmank7]

you can build your own solution https://arkapp.medium.com/how-to-use-shared-preferences-the-easy-and-fastest-way-98ce2013bf51