test_slack_importer: Fix strict_optional errors.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

mypy.ini

@@ -40,8 +40,6 @@ strict_optional = True
 
 # Tests (may be many issues in file; comment is just one error noted)
 
-[mypy-zerver/tests/test_slack_importer]  #70: error: Argument 1 to "MockResponse" has incompatible type "None"; expected "Dict[str, Any]"
-strict_optional = False
 [mypy-zerver/tests/test_service_bot_system]  #312: error: Argument 1 to "set_bot_config" has incompatible type "Optional[UserProfile]"; expected "UserProfile"
 strict_optional = False
 [mypy-zerver/tests/test_outgoing_webhook_system]  #33: error: Argument 1 to "MockServiceHandler" has incompatible type "None"; expected "str"

zerver/tests/test_slack_importer.py

@@ -1,7 +1,7 @@
 import logging
 import os
 import shutil
-from typing import Any, Dict, Iterator, List, Set, Tuple
+from typing import Any, Dict, Iterator, List, Optional, Set, Tuple
 from unittest import mock
 from unittest.mock import ANY, call
 
@@ -50,11 +50,11 @@ def remove_folder(path: str) -> None:
         shutil.rmtree(path)
 
 class MockResponse:
-    def __init__(self, json_data: Dict[str, Any], status_code: int) -> None:
+    def __init__(self, json_data: Optional[Dict[str, Any]], status_code: int) -> None:
         self.json_data = json_data
         self.status_code = status_code
 
-    def json(self) -> Dict[str, Any]:
+    def json(self) -> Optional[Dict[str, Any]]:
         return self.json_data
 
 # This method will be used by the mock to replace requests.get