Fix html file crash, simplify code. Fixes #3071

Author: cyberw

Diff for: locust/html.py

@@ -16,22 +16,14 @@
 
 
 def process_html_filename(options) -> None:
-    num_users = options.num_users
-    spawn_rate = options.spawn_rate
-    run_time = options.run_time
-
     option_mapping = {
-        "{u}": num_users,
-        "{r}": spawn_rate,
-        "{t}": run_time,
+        "{u}": options.num_users,
+        "{r}": options.spawn_rate,
+        "{t}": options.run_time,
     }
-
-    html_filename = options.html_file
-
     for option_term, option_value in option_mapping.items():
-        html_filename = html_filename.replace(option_term, str(int(option_value)))
-
-    options.html_file = html_filename
+        if option_value is not None:
+            options.html_file = options.html_file.replace(option_term, str(int(option_value)))
 
 
 def render_template_from(file, build_path=DEFAULT_BUILD_PATH, **kwargs):

Diff for: locust/test/test_html_filename.py

@@ -40,3 +40,15 @@ def test_process_html_filename_no_replacement(self):
 
         expected_filename = "static_report.html"
         self.assertEqual(mock_options.html_file, expected_filename)
+
+    def test_process_html_filename_None_arguments(self):
+        mock_options = MagicMock()
+        mock_options.num_users = 5
+        # mock_options.spawn_rate = None
+        mock_options.run_time = None
+        mock_options.html_file = "report_u{u}_r{r}_t{t}.html"
+
+        process_html_filename(mock_options)
+
+        expected_filename = "report_u5_r1_t{t}.html"
+        self.assertEqual(mock_options.html_file, expected_filename)