Check for existence of file before deleting it
Remove 'return' statement in favour of a NULL value
Copy local file if it exists and obtain boolean value
Extract the downloaded data file
Remove the .gz file from the working folder if it exists
Add downloaded file to 'files' list; return NULL otherwise
Modify whitespace and indentation
Replace 'i' index with 'j' index
Get list of CSV files that were created
Return the list of created CSV files