improve required field handling

app/controllers/submit_form_controller.rb

@@ -72,6 +72,10 @@ class SubmitFormController < ApplicationController
     Submitters::SubmitValues.call(submitter, params, request)
 
     head :ok
+  rescue Submitters::SubmitValues::RequiredFieldError => e
+    Rollbar.warning("Required field #{submitter.id}: #{e.message}") if defined?(Rollbar)
+
+    render json: { field_uuid: e.message }, status: :unprocessable_entity
   rescue Submitters::SubmitValues::ValidationError => e
     render json: { error: e.message }, status: :unprocessable_entity
   end