Fix that assert errors in commands (eg. trying to unlink node with only 1 parent) does not display the actual error message in the notification area (instead shows: ApolloError: Server response was missing for query 'undefined'.)

Fix that assert errors in commands (eg. trying to unlink node with only 1 parent) does not display the actual error message in the notification area (instead shows: ApolloError: Server response was missing for query 'undefined'.) #249