Files exported from google drive sometimes do not contain content header fields

I have an application that downloads files from google drive, exported as pdf files using GTMHTTPFetcher

.

All files are loading correctly, but the fetcher property response.expectedContentLength

returns -1 for some files. The response is also missing a content length field for these files.

I tried setting "Accept-Encoding" to "" in the request header, but that doesn't solve the problem.

Any ideas how to fix this?