The listener port cannot be disabled when setting peers_from_control_…

…nodes

If the port is explicitly set to null (causing any ReceptorAddress to
be deleted), then that's a validation error.

If the port is left off but a ReceptorAddress doesn't already exist,
we should not infer a port number and that is also a validation error.

awx/api/serializers.py

@@ -5710,7 +5710,8 @@ def check_peers_changed():
 
         # cannot enable peers_from_control_nodes if listener_port is not set
         if attrs.get('peers_from_control_nodes'):
-            if not attrs.get('listener_port') and self.instance and self.instance.canonical_address_port is None:
+            port = attrs.get('listener_port', -1)  # -1 denotes missing, None denotes explicit null
+            if (port is None) or (port == -1 and self.instance and self.instance.canonical_address is None):
                 raise serializers.ValidationError(_("Cannot enable peers_from_control_nodes if listener_port is not set."))
 
         return super().validate(attrs)