fetchData call fails if no object returned at end

[rguldener]

As reported on the community: nango dryrun throws an error if one tries to dryrun a script which doesn't return anything at the end.
The syncs also fail on Nango cloud for the same reason.

export default async function fetchData(
  nango: NangoSync
): Promise<void> {

// Function

}

Workaround for now:
Use the old format with the return { 'Model': [] }

Since we want to move to this format this should be fixed :)

[khaliqgant]

Requires an undefined check here: https://github.com/NangoHQ/nango/blob/master/packages/shared/lib/services/sync/run.service.ts#L230

if (userDefinedResults &&

Also need to signal that the script is finished ending so the log can be terminated and the webhook can be sent

Related to #912