fix: the search content return tuple issue (#555)

src/graph/nodes.py

@@ -53,6 +53,9 @@ def background_investigation_node(state: State, config: RunnableConfig):
         searched_content = LoggedTavilySearch(
             max_results=configurable.max_search_results
         ).invoke(query)
+        # check if the searched_content is a tuple, then we need to unpack it
+        if isinstance(searched_content, tuple):
+            searched_content = searched_content[0]
         if isinstance(searched_content, list):
             background_investigation_results = [
                 f"## {elem['title']}\n\n{elem['content']}" for elem in searched_content