fix(filter-nil): improve type guard for filtering null and undefined values from enums (#660)

Author: endlacer

libs/ngxtension/filter-nil/src/filter-nil.ts

@@ -1,7 +1,12 @@
 import { filter } from 'rxjs';
 
+// TypeScript's built-in `NonNullable` doesn't distribute properly over generic type parameters
+// in type predicate contexts, causing the type guard to fail. This custom conditional type
+// forces distribution by being evaluated directly in the generic context.
+type NotNullable<T> = T extends null | undefined ? never : T;
+
 export const filterNil = <T>() =>
 	filter(
-		(value: T): value is NonNullable<T> =>
+		(value: T): value is NotNullable<T> =>
 			value !== undefined && value !== null,
 	);