feat(getPageContentText): add null checks for block references

- Add validation for transclusion reference pointer existence
- Return empty string when block is not found
- Prevent potential errors from undefined block references

lib/notion/getPageContentText.js

@@ -56,7 +56,7 @@ export function getPageContentText(post, pageBlockMap) {
     const result = []
     const blockPointer = block.format.transclusion_reference_pointer
     const blockPointerId = blockPointer.id
-    if (blockPointer) {
+    if (blockPointer && pageBlockMap.block[blockPointerId].value) {
       const blockContentList = pageBlockMap.block[blockPointerId].value.content
       for (const blockContent of blockContentList) {
         result.push(getBlockContentText(blockContent))
@@ -67,6 +67,9 @@ export function getPageContentText(post, pageBlockMap) {
 
   function getBlockContentText(id) {
     const block = pageBlockMap?.block[id].value
+    if (!block) {
+      return ''
+    }
     const blockType = block.type
     // todo: 处理更多类型
     switch (blockType) {