fix: type error

Author: sxzz

src/Repl.vue

@@ -73,7 +73,7 @@ const outputSlotName = computed(() => (props.layoutReverse ? 'left' : 'right'))
 provide(injectKeyProps, toRefs(props))
 provide(
   injectKeyPreviewRef,
-  computed(() => outputRef.value?.previewRef?.container),
+  computed(() => outputRef.value?.previewRef?.container ?? null),
 )
 
 /**

src/types.ts

@@ -18,5 +18,5 @@ export type OutputModes = 'preview' | EditorMode
 export const injectKeyProps: InjectionKey<ToRefs<Required<Props>>> =
   Symbol('props')
 export const injectKeyPreviewRef: InjectionKey<
-  ComputedRef<HTMLDivElement | undefined>
+  ComputedRef<HTMLDivElement | null>
 > = Symbol('preview-ref')