Previously, there were no arguments after `memo`, so it could always just be
omitted. Now the `privacyPolicy` is there, so it’s necessary to be able to
explicitly omit the memo.
Using `"F6"` would work in some situations, but while it encodes the “no memo”
case, the internal checks that ensure we don’t try to send a memo to transparent
recipients fail on it. And as we can’t merge to a taddr without specifying
`"AllowRevealedRecipients"`, this prevents merging to taddrs (unless the
deprecated `legacy_privacy` feature is enabled).
This change makes it possible to send `null` as the `memo` argument, which
indicates “no memo” successfully. It does the same for `*_limit` parameters in
`z_mergetoaddress` and `z_shieldcoinbase` (even though those don’t have a
similar failure case), since those parameters also need to be specified when the
`privacyPolicy` is, and it’s consistent with #6599, rather than hardcoding some
particular value.
This also fixes a bug in `WalletTxBuilder` that could inadvertently require
`AllowRevealedAmounts` on a transaction from a shielded pool to itself (via
`NetAmountRecipient`).
The p2p_nu_peer_management and rewind_index RPC tests still start from
Sprout, because they are explicitly (and only) testing network behaviour
across network upgrades.
The mempool_tx_input_limit test is removed because the flag has been
ignored since Sapling activation, and will be removed at some point in
the near future.
Greg Pfeil
Daira Emma Hopwood
Kris Nuttycombe
mdr0id
Jack Grigg
Eirik Ogilvie-Wigley