Add rudimentary error handling to POST requests

import_md/hedgedoc_import.py

@@ -77,6 +77,8 @@ def process_archive_export(archive_file, instance_url, lookup_map, session_id, u
                               "creating a new, random path")
                         new_url = import_single_document(instance_url, "", document_content, session_id)
                         print(f"New URL after document migration without migrating the URL/subpath: {new_url}")
+                    else:
+                        raise SystemExit("Could not create document. Please check your session cookie. Aborting...")
                 urls_to_visit.append(new_url)
                 print()
             else: