C++ Transition Guide for 4.18

[RyuMaster]

In 4.17, inside one of my plugins, I have this line:

TSubclassOf<class UWalletWidgetBase> castToClass;

and it works. For 4.18, it gives ‘undefined class TSubclassOf<class UWalletWidgetBase> error’; Is it my possible mistake somewhere else, or something changed about how 4.18 handles this stuff?