@ANKIT PATELUsername is a required field in all of the NiFi FTP processors (GetFTP, ListFTP, and FetchFTP). Connecting to a FTP endpoint that does not require a username may require you to write your own custom processor implementation.
Another option might be to use one of the NiFi Scripting processors that calls a custom script you would need to write to return files from your FTP server.
Thank you,
Matt