Trivial typing fix

mypy cannot infer the type of an empty dict. We need to explicitly type it.

Signed-off-by: Stephen Finucane <stephen@that.guru>

Author: stephenfin

tests/test_content_type.py

@@ -54,7 +54,8 @@ def test_json_content(self):
         # The JSON content type represents implictly UTF-8 application/json.
         self.assertThat(JSON.type, Equals("application"))
         self.assertThat(JSON.subtype, Equals("json"))
-        self.assertThat(JSON.parameters, Equals({}))
+        expected_parameters: dict[str, str] = {}
+        self.assertThat(JSON.parameters, Equals(expected_parameters))
 
 
 def test_suite():