NameError when calling webhook

Not sure how yet but this exception

```
Module ZPublisher.WSGIPublisher, line 181, in transaction_pubevents
Module ZPublisher.WSGIPublisher, line 391, in publish_module
Module ZPublisher.WSGIPublisher, line 285, in publish
Module ZPublisher.mapply, line 98, in mapply
Module ZPublisher.WSGIPublisher, line 68, in call_object
Module plone.rest.service, line 21, in __call__
Module plone.restapi.services, line 19, in render
Module plone.restapi.services.content.update, line 32, in reply
Module plone.restapi.deserializer.dxcontent, line 79, in __call__
Module zope.event, line 33, in notify
Module zope.component.event, line 27, in dispatch
Module zope.component._api, line 146, in subscribers
Module zope.interface.registry, line 446, in subscribers
Module zope.interface.adapter, line 896, in subscribers
Module plone.app.contentrules.handlers, line 183, in modified
Module plone.app.contentrules.handlers, line 144, in execute_rules
Module plone.app.contentrules.handlers, line 125, in execute
Module plone.contentrules.engine.executor, line 36, in __call__
Module plone.contentrules.rule.rule, line 52, in __call__
Module collective.webhook.actions.webhook, line 151, in __call__
Module collective.webhook.actions.webhook, line 120, in interpolate
NameError: name 'unicode' is not defined
```