Reproduce:

• Create an empty event-based process
• Add a link intermediate throw event
• select the event node in the diagram

Observed:
Mapping cleanup endpoint fails with the following error:

Expected:
Mapping cleanup works normally for such nodes and no notification error is shown

There is a potential bug with the modeling library in that it doesn't assign a default value to the `name` property of link events. This means that we have problems whenever trying to parse models containing link events, as they fail validation through missing that property.

ATs:

• Create bug issue with bpmn-js: https://github.com/bpmn-io/bpmn-js/issues/1296
• Handle parsing errors in backend and return errors as 400 instead of 500
• Add documentation that we don't currently support link events
• Create ticket to stop link events being mappable: https://jira.camunda.com/browse/OPT-3476