If the data source returns a row with no columns, upload requests for screens that have an Upload Mode of 'Synchronous if available and popup on synchronous response' or 'Synchronous upload and popup on response' can show the user a 'There is no row at position 0' error.
With the REST plugin, you can check for this scenario and adjust the response to conform to what the Verivo AppServer expects. Use the following Python script to perform this check:
if(response.Rows.Count!=0 and response.Columns.Count==0):
plugin.PrintToLogger(30,"Clearing out rows");