How can I throw compile-time BP error? (through c++)

I want to throw BP error in compile-time when specific property is null.
Is there any way to do through c++? (like overriding OnRegister, PostLoad, InitializeComponent…)

This would help to enforce particular rules and avoid user errors. I’d like to know this too.

You need to create a custom K2Node.

Call UK2Node::Message_Error and UK2Node::Message_Warn to output blueprint compile errors.

You can also create custom Pins on your K2Node to validate specific input types.

Also have a look at FNodeHandlingFunctor.

Related question about creating a K2Node: Custom Blueprint K2Node Creation: Node doesn't show up - Blueprint - Unreal Engine Forums