don't try to split along ', '

sphinx/util/docfields.py

@@ -322,6 +322,8 @@ class DocFieldTransformer:
             if typedesc.is_typed:
                 try:
                     argtype, argname = fieldarg.split(None, 1)
+                    if argtype.endswith(","):
+                        raise ValueError
                 except ValueError:
                     pass
                 else: