Inbox filters with some conditions are not saved

If you use a Header-based condition at the time of saving the window gets stuck on loading

Steps to reproduce

• create a new filter
• add as a rule based on the header (see attached image)
• save and close

Expected behaviour

• the filter is saved and generated on the sieve server

Actual behaviour

• the window gets stuck loading and in the browser console reports the error attached (Error-browser.png)

Thanks to Emiliano Vavassori (Ticket #146788)