lncli: remove requirement for invoice value argument

cmd/lncli/commands.go

@@ -1168,9 +1168,10 @@ var addInvoiceCommand = cli.Command{
 	Usage: "add a new invoice.",
 	Description: `
 	Add a new invoice, expressing intent for a future payment.
-	
-	The number of satoshis in this invoice is necessary for the creation, 
-	the remaining parameters are optional.`,
+
+	Invoices without an amount can be created by not supplying any
+	parameters or providing an amount of 0. These invoices allow the payee
+	to specify the amount of satoshis they wish to send.`,
 	ArgsUsage: "value preimage",
 	Flags: []cli.Flag{
 		cli.StringFlag{
@@ -1239,8 +1240,6 @@ func addInvoice(ctx *cli.Context) error {
 		if err != nil {
 			return fmt.Errorf("unable to decode amt argument: %v", err)
 		}
-	default:
-		return fmt.Errorf("amt argument missing")
 	}
 
 	switch {