fix(api): Create workaround for null union with multiple types (#64834)

See comment in code for detail

src/sentry/apidocs/spectacular_ports.py

@@ -146,7 +146,18 @@ def resolve_type_hint(hint) -> Any:
         else:
             schema = resolve_type_hint(type_args[0])
         if type(None) in args:
-            schema["nullable"] = True
+            # There's an issue where if 3 or more types are OR'd together and one of
+            # them is None, validating the schema will fail because "nullable: true"
+            # with "anyOf" raises an error because there is no "type" key on the
+            # schema. This works around it by including a proxy null object in
+            # the "anyOf".
+            # See:
+            #   - https://github.com/tfranzel/drf-spectacular/issues/925
+            #   - https://github.com/OAI/OpenAPI-Specification/issues/1368.
+            if len(args) > 2:
+                schema["oneOf"].append({"type": "object", "nullable": True})
+            else:
+                schema["nullable"] = True
         return schema
     elif origin is collections.abc.Iterable:
         return build_array_type(resolve_type_hint(args[0]))