fixes bug in union type checking

Author: tclose

pydra/utils/typing.py

@@ -527,7 +527,7 @@ def check_union(tp, pattern_args):
                         except TypeError as e:
                             reasons.append(e)
                         else:
-                            reasons = None
+                            reasons = []
                             break
                     if self.match_any_of_union and len(reasons) < len(tp_args):
                         # Just need one of the union args to match