fix: handle empty FallbackSearchResult to prevent TypeError

[DaveOkpare]

A bug was encountered where the application threw a TypeError: Cannot read properties of undefined (reading 'length') when attempting to access the length of fallbackSearchResults if it was uninitialized or empty.

Fix:

• Added a reducer function to the fallbackSearchKeyPersons annotation to properly merge state and update.
• Provided a default value for fallbackSearchKeyPersons, ensuring it initializes to an empty array ([]) if no data is present.

[mayooear]

what was the query that lead to this? Send screenshots and/or url to langsmith traces from the run.

type FallbackSearchResult = z.infer<typeof fallbackSearchResultSchema> should be a default empty array.

[DaveOkpare]

@mayooear Here are the traces and screenshot from Langgraph Studio.

You can replicate it by using https://vespa.ai as inputUrl.

error:   ┏ Background run failed:
TypeError: Cannot read properties of null (reading 'length')
    at RunnableCallable.generateReportNode (/workspaces/ai-company-researcher/src/nodes/generateReport.ts:72:29)
      70 |
      71 |   // If no fallback results, remove the entire SEARCH_RESULTS section
    > 72 |   if (fallbackSearchResults.length === 0) {
         |                             ^
      73 |     prompt = prompt.replace('{SEARCH_RESULTS}', '');
      74 |   } else {
      75 |     prompt = prompt.replace(
    at file:///workspaces/ai-company-researcher/node_modules/@langchain/langgraph/dist/utils.js:79:113