Get rid of ambiguous OutputType::NONE value

Based on suggestion by Pieter Wuille <pieter.wuille@gmail.com> at
https://github.com/bitcoin/bitcoin/pull/12119#issuecomment-357982763

After #12119, the NONE output type was overloaded to refer to either an output
type that couldn't be parsed, or to an automatic change output mode.  This
change drops the NONE enum and uses a simple bool indicate parse failure, and a
new CHANGE_AUTO enum to refer the change output type.

This change is almost a pure refactoring except it makes RPCs reject empty
string ("") address types instead of treating them like they were unset. This
simplifies the parsing code a little bit and could prevent RPC usage mistakes.
It's noted in the release notes.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/qt/paymentserver.cpp b/src/qt/paymentserver.cpp
index 926a699754..275dba0b15 100644
--- a/src/qt/paymentserver.cpp
+++ b/src/qt/paymentserver.cpp
@@ -648,7 +648,7 @@ void PaymentServer::fetchPaymentACK(WalletModel* walletModel, const SendCoinsRec
         // use for change. Despite an actual payment and not change, this is a close match:
         // it's the output type we use subject to privacy issues, but not restricted by what
         // other software supports.
-        const OutputType change_type = walletModel->wallet().getDefaultChangeType() != OutputType::NONE ? walletModel->wallet().getDefaultChangeType() : walletModel->wallet().getDefaultAddressType();
+        const OutputType change_type = walletModel->wallet().getDefaultChangeType() != OutputType::CHANGE_AUTO ? walletModel->wallet().getDefaultChangeType() : walletModel->wallet().getDefaultAddressType();
         walletModel->wallet().learnRelatedScripts(newKey, change_type);
         CTxDestination dest = GetDestinationForKey(newKey, change_type);
         std::string label = tr("Refund from %1").arg(recipient.authenticatedMerchant).toStdString();