zulip_tools: Make default default_value be None, not "".

scripts/lib/upgrade-zulip-stage-2

@@ -272,7 +272,7 @@ class_renames = {
     "zulip::rabbit": "zulip::profile::rabbitmq",
     "zulip::voyager": "zulip::profile::standalone",
 }
-classes = re.split(r"\s*,\s*", get_config(config_file, "machine", "puppet_classes"))
+classes = re.split(r"\s*,\s*", get_config(config_file, "machine", "puppet_classes", ""))
 new_classes = [class_renames.get(c, c) for c in classes if c != "zulip::base"]
 if classes != new_classes:
     if args.skip_restart:

scripts/lib/zulip_tools.py

@@ -16,7 +16,7 @@ import sys
 import time
 import uuid
 from datetime import datetime, timedelta
-from typing import IO, Any, Dict, List, Sequence, Set, Union, overload
+from typing import IO, Any, Dict, List, Optional, Sequence, Set, Union, overload
 from urllib.parse import SplitResult
 
 DEPLOYMENTS_DIR = "/home/zulip/deployments"
@@ -585,7 +585,17 @@ def assert_running_as_root(strip_lib_from_paths: bool = False) -> None:
 
 @overload
 def get_config(
-    config_file: configparser.RawConfigParser, section: str, key: str, default_value: str = ""
+    config_file: configparser.RawConfigParser,
+    section: str,
+    key: str,
+    default_value: None,
+) -> Optional[str]: ...
+@overload
+def get_config(
+    config_file: configparser.RawConfigParser,
+    section: str,
+    key: str,
+    default_value: str,
 ) -> str: ...
 @overload
 def get_config(
@@ -595,8 +605,8 @@ def get_config(
     config_file: configparser.RawConfigParser,
     section: str,
     key: str,
-    default_value: Union[str, bool] = "",
-) -> Union[str, bool]:
+    default_value: Union[str, bool, None] = None,
+) -> Union[str, bool, None]:
     if config_file.has_option(section, key):
         val = config_file.get(section, key)
         if isinstance(default_value, bool):