Models::areRelated should check if model has content

[DivineOmega]

It is currently possible to use this method with newly created models that have not yet been stored in the database. This makes no sense as models that are not stored can not be related.

If a model that is not stored is passed to this method an IllegalArgumentException should be thrown.

[dextermb]

Could loop through and check the attribute exists on each model, if false then throw the exception

[DivineOmega]

That should work. 👍