Guard the content field against empty strings so adding it in the UI
without a value no longer sends content: "" to the API, which is not
valid ProseMirror content. This matches the existing defaultApproverIds
guard.
Also expose title, classification, and document type on the update
operation. Like content, these edit the current draft version, creating
one from the latest published version when none exists.
Signed-off-by: Sacha Al Himdani <sacha@probo.com>
909c54033c