diff --git a/swh/__init__.py b/swh/__init__.py
--- a/swh/__init__.py
+++ b/swh/__init__.py
@@ -1,4 +1,3 @@
 from pkgutil import extend_path
-from typing import List
 
-__path__: List[str] = extend_path(__path__, __name__)
+__path__ = extend_path(__path__, __name__)
diff --git a/swh/web/__init__.py b/swh/web/__init__.py
--- a/swh/web/__init__.py
+++ b/swh/web/__init__.py
@@ -1,4 +1,3 @@
 from pkgutil import extend_path
-from typing import List
 
-__path__: List[str] = extend_path(__path__, __name__)
+__path__ = extend_path(__path__, __name__)
diff --git a/swh/web/api/apiresponse.py b/swh/web/api/apiresponse.py
--- a/swh/web/api/apiresponse.py
+++ b/swh/web/api/apiresponse.py
@@ -227,5 +227,5 @@
     """Custom DRF exception handler used to generate API error responses.
     """
     sentry_capture_exception(exc)
-    doc_data = getattr(exc, "doc_data", None)
+    doc_data = getattr(exc, "doc_data", {})
     return error_response(context["request"], exc, doc_data)
diff --git a/tox.ini b/tox.ini
--- a/tox.ini
+++ b/tox.ini
@@ -26,7 +26,7 @@
 extras =
   testing
 deps =
-  mypy
+  mypy==0.920
 commands =
   mypy swh