Allow passing an empty string for purchaseticket addresses

The purchaseticket RPC would previously fail if the ticket address
or pool address was undeclared (), not allowing the end user to
set the ticket expiry if either was absent. This corrects this
problem by skipping assignment if it is .

rpc/legacyrpc/methods.go

@@ -2331,11 +2331,13 @@ func PurchaseTicket(icmd interface{}, w *wallet.Wallet) (interface{}, error) {
 	// Set ticket address if specified.
 	var ticketAddr dcrutil.Address
 	if cmd.TicketAddress != nil {
-		addr, err := decodeAddress(*cmd.TicketAddress, w.ChainParams())
-		if err != nil {
-			return nil, err
+		if *cmd.TicketAddress != "" {
+			addr, err := decodeAddress(*cmd.TicketAddress, w.ChainParams())
+			if err != nil {
+				return nil, err
+			}
+			ticketAddr = addr
 		}
-		ticketAddr = addr
 	}
 
 	numTickets := 1
@@ -2349,20 +2351,22 @@ func PurchaseTicket(icmd interface{}, w *wallet.Wallet) (interface{}, error) {
 	var poolAddr dcrutil.Address
 	var poolFee dcrutil.Amount
 	if cmd.PoolAddress != nil {
-		addr, err := decodeAddress(*cmd.PoolAddress, w.ChainParams())
-		if err != nil {
-			return nil, err
-		}
-		poolAddr = addr
+		if *cmd.PoolAddress != "" {
+			addr, err := decodeAddress(*cmd.PoolAddress, w.ChainParams())
+			if err != nil {
+				return nil, err
+			}
+			poolAddr = addr
 
-		// Attempt to get the amount to send to
-		// the pool after.
-		if cmd.PoolFees == nil {
-			return nil, fmt.Errorf("gave pool address but no pool fee")
-		}
-		poolFee, err = dcrutil.NewAmount(*cmd.PoolFees)
-		if err != nil {
-			return nil, err
+			// Attempt to get the amount to send to
+			// the pool after.
+			if cmd.PoolFees == nil {
+				return nil, fmt.Errorf("gave pool address but no pool fee")
+			}
+			poolFee, err = dcrutil.NewAmount(*cmd.PoolFees)
+			if err != nil {
+				return nil, err
+			}
 		}
 	}