upload to s3 fails if last chunk in finish happens to be of 0 length

Multipart upload to s3 fails in finish method when last chunk is set to zero length, this happens if original buffer size is between 
MIN_WRITE_SIZE = 5 * 1024 * 1024
MAX_WRITE_SIZE = 5 * 1024 * 1024 * 1024
from put()