Should not enter error code variable before an error is selected

[ingorichtsmeier]

For an attached boundary event, I can enter the Error code variable and the Error Message variable without selecting an error in the drop down.

This leads to errors in the process execution on the camunda engine.

Steps to Reproduce

Steps to reproduce the behavior:

1. model a task
2. attach an error bounday event
3. fill the Error code variable and Error message variable (without selecting an error in the dropdown)

Expected Behavior

The fields should be disabled until an error is selected in the dropdown.

Environment

Please complete the following information:

• OS: [e.g. MacOS 10.2, Windows 10] Windows10
• Camunda Modeler Version: [e.g. 2.0.0] 3.0.0.beta2

[pinussilvestrus]

Thanks for your contribution! Will be a little nice improvement to ensure parity with the engine.

It will probably need a fix inside the bpmn-js-properties-panel.