fixup! Change default properties from null to undefined (#662)

Author: lukasbriza

src/components/Modal/_hooks/useModalFocus.js

@@ -16,7 +16,7 @@ export const useModalFocus = (
 
       const dialogElement = dialogRef.current;
 
-      if (dialogElement == null) {
+      if (dialogElement === undefined) {
         return () => {};
       }