How to detect document/report refresh has no content using RESTful API and SDK

Hi Experts,

I am using:

1) ReportEngine SDK to refresh and save document to TEXT file.

2) RESTful API to refresh and saved to PDF and XLS files.

But some time the document has no content when I save those files.  How can I detect if there are no content, I do not have to save them.  We cannot send the files to clients without content.  The files have some bytes; they are not 0 bytes.

Thank you.