Fix AtLeastOneAmong rule

src/jflow/rules.py

@@ -260,7 +260,7 @@ class AtLeastOneAmong(LinkRule):
         if self.parameter_value is None or not self.parameter_value:
             has_one = False
             for grp_param in self.targets_args:
-                if not getattr(self.wf_instance, grp_param).is_None:
+                if grp_param in self.user_args and self.user_args[grp_param]:
                     has_one = True
                     break
             if not has_one: