UI should inform about error on the query execution.

For instance, the request I made returned the following error:
{"errors":[{"message":"Cannot return null for non-nullable type: 'DateTime' within parent 'ProcessInstance' (/ProcessInstances[0]/lastUpdate)","path":["ProcessInstances",0,"lastUpdate"],"extensions":{"classification":"DataFetchingException"}},{"message":"Cannot return null for non-nullable type: 'String' within parent 'ProcessInstance' (/ProcessInstances[0]/endpoint)","path":["ProcessInstances",0,"endpoint"],"extensions":{"classification":"DataFetchingException"}}],"data":

}