--- a/src/pyams_content/shared/common/interfaces/__init__.py	Fri Oct 04 19:19:45 2019 +0200
+++ b/src/pyams_content/shared/common/interfaces/__init__.py	Mon Oct 07 13:38:33 2019 +0200
@@ -307,7 +307,8 @@
 
     owners = PrincipalsSet(title=_("Substitute for"),
                            description=_("Contributor will have access to contents owned by these "
-                                         "principals"))
+                                         "principals"),
+                           required=False)
 
     def check_access(self, context, permission=MANAGE_CONTENT_PERMISSION, request=None):
         """Check if principal is granted access to given context"""