fix(runtime-dom): fix crash when modifier is empty

Author: baiwusanyu-c

packages/runtime-dom/src/directives/vOn.ts

@@ -35,9 +35,13 @@ const modifierGuards: Record<
 export const withModifiers = <
   T extends (event: Event, ...args: unknown[]) => any
 >(
-  fn: T & { _withMods?: { [key: string]: T } },
+  fn: T & { _withMods?: { [key: string]: T } } ,
   modifiers: string[]
 ) => {
+
+  if(!fn) {
+    return
+  }
   const cache = fn._withMods || (fn._withMods = {})
   const cacheKey = modifiers.join('.')
   return (