fix(runtime-core): ensure mergeProps skips undefined event handlers (#5299)

fix #5296

packages/runtime-dom/src/modules/events.ts

@@ -141,7 +141,7 @@ function patchStopImmediatePropagation(
       originalStop.call(e)
       ;(e as any)._stopped = true
     }
-    return value.map(fn => (e: Event) => !(e as any)._stopped && fn(e))
+    return value.map(fn => (e: Event) => !(e as any)._stopped && fn && fn(e))
   } else {
     return value
   }