Correctly serialize empty content_type for blobs.

A BlobDataHandle could not have a content_type set, but that should be
treated no different from an empty string, so serialize it as such.
Otherwise this will trigger validation failures causing weird behavior
when for example a blob without a content type is posted on a

(cherry picked from commit bb84d169288460af40536ebbe0303cb35f11a5a1)

Bug: 813146
Change-Id: I0a20a6b91391e9aa490a337b93c74f9ab4316e31
Commit-Queue: Marijn Kruisselbrink <>
Reviewed-by: Daniel Cheng <>
Cr-Original-Commit-Position: refs/heads/master@{#537462}
Reviewed-by: Marijn Kruisselbrink <>
Cr-Commit-Position: refs/branch-heads/3325@{#520}
Cr-Branched-From: bc084a8b5afa3744a74927344e304c02ae54189f-refs/heads/master@{#530369}
1 file changed