hosts can be list or string

lib/ansible/playbook/play.py

@@ -106,7 +106,10 @@ class Play(Base, Taggable, Become):
     @staticmethod
     def load(data, variable_manager=None, loader=None):
         if ('name' not in data or data['name'] is None) and 'hosts' in data:
-            data['name'] = data['hosts']
+            if isinstance(data['hosts'], list):
+                data['name'] = ','.join(data['hosts'])
+            else:
+                 data['name'] = data['hosts']
         p = Play()
         return p.load_data(data, variable_manager=variable_manager, loader=loader)