모달 닫기 버튼 에러

모달 띄우는 부분은 잘되는데 닫는부분에서 에러가 나는데요 

이유를 모르겠습니다.

콘솔창에서는 

runtime-core.esm-bundler.js:38 [Vue warn]: Unhandled error during execution of native event handler 
  at <BaseTransition appear=false persisted=false mode=undefined  ... > 
  at <Transition createAt=undefined > 
  at <AppModal modelValue=true onUpdate:modelValue=fn title="게시글"  ... > 
  at <PostModal modelValue=true onUpdate:modelValue=fn title="안녕하세요11"  ... > 
  at <PostListView onVnodeUnmounted=fn<onVnodeUnmounted> ref=Ref< Proxy {__v_skip: true} > > 
  at <RouterView> 
  at <TheView> 
  at <App>
warn @ runtime-core.esm-bundler.js:38
logError @ runtime-core.esm-bundler.js:212
handleError @ runtime-core.esm-bundler.js:204
callWithErrorHandling @ runtime-core.esm-bundler.js:158
callWithAsyncErrorHandling @ runtime-core.esm-bundler.js:164
invoker @ runtime-dom.esm-bundler.js:369
runtime-core.esm-bundler.js:218 Uncaught TypeError: str.charAt is not a function
    at shared.esm-bundler.js:552:53
    at shared.esm-bundler.js:534:37
    at shared.esm-bundler.js:556:62
    at shared.esm-bundler.js:534:37
    at emit$1 (runtime-core.esm-bundler.js:668:40)
    at runtime-core.esm-bundler.js:7348:53
    at ComputedRefImpl.set [as _setter] (PostModal.vue:42:3)
    at set value [as value] (reactivity.esm-bundler.js:1149:14)
    at closeModal (PostModal.vue:48:13)
    at callWithErrorHandling (runtime-core.esm-bundler.js:155:22)

postmodal.vue