TxOutputType.multisig should be optional, not repeated

protob/types.proto

@@ -165,7 +165,7 @@ message TxOutputType {
 	repeated uint32 address_n = 2;			// BIP-32 path to derive the key from master node; has higher priority than "address"
 	required uint64 amount = 3;			// amount to spend in satoshis
 	required OutputScriptType script_type = 4;	// output script type
-	repeated MultisigRedeemScriptType multisig = 5; // Defines multisig address; script_type must be PAYTOMULTISIG
+	optional MultisigRedeemScriptType multisig = 5; // Defines multisig address; script_type must be PAYTOMULTISIG
 }
 
 /**