fix validation with custom type (#1627)
fix validation with custom type (#1627)

* fix validation with custom type

* fix lint

superdesk/superdesk-core,petrjasek/superdesk-core,petrjasek/superdesk-core,superdesk/superdesk-core,petrjasek/superdesk-core,superdesk/superdesk-core,superdesk/superdesk-core,petrjasek/superdesk-core