AFAICT (at least as of the first commit in the PR), this NULL AS from_account_id is preserved, because there is still an asymmetry between transparent and shielded (we are not inserting transactions into both sent and received tables for transparent, in the same way we do for shielded). I think that asymmetry needs fixing prior to the next release (if not in this PR).
_Originally posted by @str4d in https://github.com/zcash/librustzcash/pull/1402#discussion_r1648028219_
_See also https://github.com/zcash/librustzcash/pull/1402#discussion_r1648037109_