file upload

Hello,
I am testing this process to upload and download files. I have set the mandatory property of upload widget to false.
When I throw the process, if I do not select a file in "Step Upload" and click "submit" the process does not continue to the next task and this message catalina log:

I understand bonita uses documents to store files uploaded by users however they are stored in the bonita database and for me this is unnacceptable. Is there a way to change this so it's stored as a file in a place I wish or is there a way to upload a file via groovy script?