From eb5af71a301fb6a388296cb2a00ceec82cf0429b Mon Sep 17 00:00:00 2001
From: David Tymon <david.tymon@gmail.com>
Date: Tue, 15 Mar 2016 13:38:55 +1100
Subject: [PATCH] JS: ATNConfig can incorrectly change "alt" of 0 to null

When an ATNConfig instance is created with an alt of 0, it is
possible for it to be incorrectly changed to null due to its
"falsey" nature.
---
 runtime/JavaScript/src/antlr4/atn/ATNConfig.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/runtime/JavaScript/src/antlr4/atn/ATNConfig.js b/runtime/JavaScript/src/antlr4/atn/ATNConfig.js
index 0b13737ed..988729dc7 100644
--- a/runtime/JavaScript/src/antlr4/atn/ATNConfig.js
+++ b/runtime/JavaScript/src/antlr4/atn/ATNConfig.js
@@ -50,7 +50,7 @@ function checkParams(params, isCfg) {
 	} else {
 		var props = {};
 		props.state = params.state || null;
-		props.alt = params.alt || null;
+		props.alt = (params.alt === undefined) ? null : params.alt;
 		props.context = params.context || null;
 		props.semanticContext = params.semanticContext || null;
 		if(isCfg) {