WIP donation

src/wallet/asyncrpcoperation_shieldcoinbase.h

@@ -49,7 +49,7 @@ public:
         std::vector<ShieldCoinbaseUTXO> inputs,
         std::string toAddress,
         CAmount fee = SHIELD_COINBASE_DEFAULT_MINERS_FEE,
-        CAmount donation,
+        CAmount donation = 0,
         UniValue contextInfo = NullUniValue);
     virtual ~AsyncRPCOperation_shieldcoinbase();