Add typing and fix a type issue in _Error._matches_type

Author: DanielNoord

jsonschema/exceptions.py

@@ -155,12 +155,18 @@ def _contents(self):
         )
         return dict((attr, getattr(self, attr)) for attr in attrs)
 
-    def _matches_type(self):
+    def _matches_type(self) -> bool:
+        if isinstance(self.schema, _utils.Unset):
+            return False
+
         try:
             expected = self.schema["type"]
         except (KeyError, TypeError):
             return False
 
+        if isinstance(self._type_checker, _utils.Unset):
+            return False
+
         if isinstance(expected, str):
             return self._type_checker.is_type(self.instance, expected)