Initialize data structure in fetch_data function and update main execution with user access key

fetch_data.py

@@ -21,6 +21,7 @@ def fetch_data(user_access_key):
         papers_data = {}
         try:
             papers_data['status'] = 'success'
+            papers_data['data'] = {}
             with ThreadPoolExecutor() as executor:
                 arxiv_future = executor.submit(fetch_arxiv_data)
                 pmc_future = executor.submit(fetch_pmc_data)
@@ -45,6 +46,6 @@ def fetch_data(user_access_key):
     return data
 
 if __name__ == '__main__':
-    data = fetch_data()
+    data = fetch_data(ACCESS_KEY)
     with open('data.json', 'w') as f:
         f.write(data)