fix(types): scrip-setup+ts: ensure proper handling of `null` as default prop value. (#4979)

fix #4868

packages/runtime-core/src/apiSetupHelpers.ts

@@ -131,6 +131,7 @@ type InferDefaults<T> = {
 }
 
 type InferDefault<P, T> = T extends
+  | null
   | number
   | string
   | boolean