Cannot upgrade template from empty one to another one

Describe the bug

When I apply an empty template to a task

And then change the empty template to match this template: https://github.com/francav/hey-duedate/blob/c8-connector/c8-connector/element-templates/template-connector.json and upgrade

Then I get an error and the template is not correctly applied and the icon is not visible:

The issue was originally opened for the Web Modeler: https://github.com/camunda/web-modeler/issues/2376

Steps to reproduce

1. Create an empty template (see empty template in attachment)
2. Create a new BPMN file
3. Add a new task, apply the empty template to it (see empty template in attachment)
4. Replace the empty template with this one: https://github.com/francav/hey-duedate/blob/c8-connector/c8-connector/element-templates/template-connector.json (see non-empty template in attachment)
5. Go back to the BPMN file from 2.
6. Select the task and choose upgrade the template in the Properties Panel to apply the new non-empty template
7. The template is not upgraded correctly, the icon is missing and I also get this error in console:

unhandled error in event listener Error: unknown binding <property> for element <Activity_1xdyi2h>, this should never happen
    at QA (index.esm.js:17840:10)
    at NA (index.esm.js:17668:9)
    at index.esm.js:18711:41
    at Array.forEach (<anonymous>)
    at UA._applyConditions (index.esm.js:18711:21)
    at UA.<anonymous> (CommandInterceptor.js:43:15)
    at EventBus.js:519:13
    at o._invokeListener (EventBus.js:371:19)
    at o._invokeListeners (EventBus.js:352:24)
    at o.fire (EventBus.js:313:24)
    at i._fire (CommandStack.js:356:29)
    at i._internalExecute (CommandStack.js:425:10)
    at i.execute (CommandStack.js:153:8)
    at Ki.updateProperties (Modeling.js:98:22)
    at LA._updateZeebeModelerTemplate (index.esm.js:17978:14)
    at LA.preExecute (index.esm.js:17930:10)
    at i._internalExecute (CommandStack.js:401:15)
    at i.execute (CommandStack.js:153:8)
    at WA.applyTemplate (index.esm.js:19140:24)
    at up (index.esm.js:19708:27)
    at action (index.esm.js:20284:19)
    at p (index.esm.js:858:5)
    at Object.onClick [as clickfalse] (index.esm.js:892:25)
    at HTMLButtonElement.B (preact.module.js:1:4348)
    at HTMLButtonElement.i (helpers.js:85:17)

Attachment

example-templates.zip

Expected behavior

The template can be upgraded correctly.

Environment

• OS: not relevant
• Camunda Modeler Version: 5.3.0
• Execution Platform: not relevant
• Installed plug-ins: not relevant

Additional context

No response

[nikku]

My assumption would be however that we do reject such templates in the first place (do not allow to choose them, as they fail validation on load). Need to investigate this.

[nikku]

The error says:

unknown binding <property>

And indeed the template contains a binding property which is not supported in Camunda 8 element templates: