[Swift] only first rule parameter generated correctly

[EXC-BAD-ACCESS]

the following grammar generates invalid code for rule2 and rule3:

grammar T;

rule1[Int arg1]
    :   .
    ;

rule2[Int arg1, Int arg2]
    :   .
    ;

rule3[Int arg1, Int arg2, Int arg3]
    :   .
    ;

=>

open func rule2(_ arg1: Int!, _arg2: Int!) throws -> Rule2Context {
open func rule3(_ arg1: Int!, _arg2: Int!, _arg3: Int!) throws -> Rule3Context {

it should generate something like:

open func rule2(_ arg1: Int!, _ arg2: Int!) throws -> Rule2Context {
open func rule3(_ arg1: Int!, _ arg2: Int!, _ arg3: Int!) throws -> Rule3Context {

(space between "_" and "arg2" / "arg3"