Fix issue where empty WebUI property is not parsed correctly

locust/test/test_web.py

@@ -764,7 +764,7 @@ def tick(self):
         response = requests.get("http://127.0.0.1:%i/stop" % self.web_port)
         self.assertEqual(response.json()["message"], "Test stopped")
 
-    def test_swarm_custom_argument(self):
+    def test_swarm_custom_argument_without_default_value(self):
         my_dict = {}
 
         class MyUser(User):
@@ -776,10 +776,10 @@ def my_task(self):
                 my_dict["val"] = self.environment.parsed_options.my_argument
 
         @locust.events.init_command_line_parser.add_listener
-        def _(parser, **kw):
+        def _(parser):
             parser.add_argument("--my-argument", type=int, help="Give me a number")
 
-        parsed_options = parse_options(args=["--my-argument", "42"])
+        parsed_options = parse_options()
         self.environment.user_classes = [MyUser]
         self.environment.parsed_options = parsed_options
         self.environment.web_ui.parsed_options = parsed_options
@@ -788,7 +788,59 @@ def _(parser, **kw):
             data={"user_count": 1, "spawn_rate": 1, "host": "", "my_argument": "42"},
         )
         self.assertEqual(200, response.status_code)
-        self.assertEqual(my_dict["val"], 42)
+        self.assertEqual("42", my_dict["val"])
+
+    def test_swarm_custom_argument_with_default_value(self):
+        my_dict = {}
+
+        class MyUser(User):
+            host = "http://example.com"
+            wait_time = constant(1)
+
+            @task(1)
+            def my_task(self):
+                my_dict["val"] = self.environment.parsed_options.my_argument
+
+        @locust.events.init_command_line_parser.add_listener
+        def _(parser):
+            parser.add_argument("--my-argument", type=int, help="Give me a number", default=24)
+
+        parsed_options = parse_options()
+        self.environment.user_classes = [MyUser]
+        self.environment.parsed_options = parsed_options
+        self.environment.web_ui.parsed_options = parsed_options
+        response = requests.post(
+            "http://127.0.0.1:%i/swarm" % self.web_port,
+            data={"user_count": 1, "spawn_rate": 1, "host": "", "my_argument": "42"},
+        )
+        self.assertEqual(200, response.status_code)
+        self.assertEqual(42, my_dict["val"])
+
+    def test_swarm_override_command_line_argument(self):
+        my_dict = {}
+
+        class MyUser(User):
+            host = "http://example.com"
+            wait_time = constant(1)
+
+            @task(1)
+            def my_task(self):
+                my_dict["val"] = self.environment.parsed_options.my_argument
+
+        @locust.events.init_command_line_parser.add_listener
+        def _(parser):
+            parser.add_argument("--my-argument", type=int, help="Give me a number")
+
+        parsed_options = parse_options(args=["--my-argument", "24"])
+        self.environment.user_classes = [MyUser]
+        self.environment.parsed_options = parsed_options
+        self.environment.web_ui.parsed_options = parsed_options
+        response = requests.post(
+            "http://127.0.0.1:%i/swarm" % self.web_port,
+            data={"user_count": 1, "spawn_rate": 1, "host": "", "my_argument": "42"},
+        )
+        self.assertEqual(200, response.status_code)
+        self.assertEqual(42, my_dict["val"])
 
     def test_swarm_host_value_not_specified(self):
         class MyUser(User):

locust/web.py

@@ -285,9 +285,9 @@ def swarm() -> Response:
                     if isinstance(parsed_options_value, bool):
                         parsed_options_dict[key] = value == "true"
                     elif parsed_options_value is None:
-                        parsed_options_dict[key] = parsed_options_value
+                        parsed_options_dict[key] = value
                     else:
-                        parsed_options_dict[key] = type(parsed_options_dict[key])(value)
+                        parsed_options_dict[key] = type(parsed_options_value)(value)
 
             if environment.shape_class and environment.runner is not None:
                 environment.runner.start_shape()