Suggested fix for plugins annotation

gistfile0.diff

diff --git a/src/twisted/application/twist/_options.py b/src/twisted/application/twist/_options.py
index d19395d78b..f0b9e48888 100644
--- a/src/twisted/application/twist/_options.py
+++ b/src/twisted/application/twist/_options.py
@@ -170,21 +170,21 @@ class TwistOptions(Options):
             self["reactor"] = self.installReactor(self["reactorName"])
 
     @property
-    def plugins(self) -> Mapping[Optional[str], IServiceMaker]:
+    def plugins(self) -> Mapping[str, IServiceMaker]:
         if "plugins" not in self:
             plugins = {}
             for plugin in getPlugins(IServiceMaker):
                 plugins[plugin.tapname] = plugin
             self["plugins"] = plugins
 
-        return cast(Mapping[Optional[str], IServiceMaker], self["plugins"])
+        return cast(Mapping[str, IServiceMaker], self["plugins"])
 
     @property
     def subCommands(
         self,
     ) -> Iterable[Tuple[str, None, Callable[[IServiceMaker], Options], str]]:
         plugins = self.plugins
-        for name in sorted(plugins, key=lambda x: (x is None, x)):
+        for name in sorted(plugins):
             plugin = plugins[name]
 
             # Don't pass plugin.options along in order to avoid resolving the
diff --git a/src/twisted/application/twist/_twist.py b/src/twisted/application/twist/_twist.py
index 6d54af46af..ea96999a67 100644
--- a/src/twisted/application/twist/_twist.py
+++ b/src/twisted/application/twist/_twist.py
@@ -102,8 +102,12 @@ class Twist:
         options = cls.options(argv)
 
         reactor = options["reactor"]
+        # If subCommand is None, TwistOptions.parseOptions() raises UsageError
+        # and Twist.options() will exit the runner, so we'll never get here.
+        subCommand = options.subCommand
+        assert subCommand is not None
         service = cls.service(
-            plugin=options.plugins[options.subCommand],
+            plugin=options.plugins[subCommand],
             options=options.subOptions,
         )
 
diff --git a/src/twisted/application/twist/test/test_twist.py b/src/twisted/application/twist/test/test_twist.py
index c503bd913f..19abae09f0 100644
--- a/src/twisted/application/twist/test/test_twist.py
+++ b/src/twisted/application/twist/test/test_twist.py
@@ -108,6 +108,7 @@ class TwistTests(twisted.trial.unittest.TestCase):
         options = Twist.options(["twist", "web"])
 
         reactor = options["reactor"]
+        assert options.subCommand is not None
         service = Twist.service(
             plugin=options.plugins[options.subCommand],
             options=options.subOptions,