diff -r 764381756899 -r 62373840e33a src/main.h
--- a/src/main.h	Wed Mar 11 19:05:34 2020 +0200
+++ b/src/main.h	Tue Mar 17 23:13:29 2020 +0200
@@ -74,13 +74,14 @@
 	using conditionaledgeid_t = Id<class ConditionalEdge>;
 	using subfileid_t = Id<class SubfileReference>;
 
-	constexpr struct
+	constexpr struct NullId
 	{
 		template<typename T>
 		constexpr operator Id<T>() const
 		{
 			return Id<T>{0};
 		}
+		static constexpr decltype(ldraw::id_t::value) value = 0;
 	} NULL_ID = {};
 
 	template<typename T>