Managing a List of structures in Test Scenario editor produces an Exception

When trying to delete an item from a list of structures with nested structures in the scenario editor, an exception is thrown with a message that is not helpful to the end user.

Log entry is:
```
[[0m[[31m17:16:51,564 ERROR [org.kie.workbench.common.services.backend.logger.GenericErrorLoggerServiceImpl] (default task-415) Error from user: xxxxx Error ID: -881202734 Location: LibraryPerspective|$ProjectScreen[!Worg.kie.dmn.decision.navigator,EDiagramEditorPropertiesScreen,Eorg.drools.scenariosimulation.TestTools?scesimeditorid=1,!Eorg.drools.scenariosimulation.TestTools?scesimeditorid=2,Eorg.docks.PlaceHolder?name=testRunnerReportingPanel,Worg.kie.guvnor.explorer,],DMNDiagramEditor?path_uri=default://master@dm-ai/XmlValidationBug/src/main/resources/Math%2520Functions.dmn&file_name=Math%20Functions.dmn&has_version_support=true,DMNDiagramEditor?path_uri=default://master@dm-ai/XmlValidationBug/src/main/resources/Divide.dmn&file_name=Divide.dmn&has_version_support=true,org.kie.workbench.common.screens.messageconsole.MessageConsole,,AddAssetsScreen,ScenarioSimulationEditor?path_uri=default://master@dm-ai/XmlValidationBug/src/test/resources/Test%2520Math%2520Functions.scesim&file_name=Test%20Math%20Functions.scesim&has_version_support=true Exception: Uncaught exception: Exception caught: (TypeError) : Cannot read property 'Tc' of undefined Caused by: (TypeError) : Cannot read property 'Tc' of undefined
```

From UI I could see: `Uncaught exception: Exception caught: (TypeError) : Cannot read property 'Tc' of undefined Caused by: (TypeError) : Cannot read property 'Tc' of undefined`