From ad83f26b5d9a5fc83962d7bef10a84c08a338af8 Mon Sep 17 00:00:00 2001
From: Zefram Lou <zeframlou@gmail.com>
Date: Wed, 22 Jan 2020 21:32:39 -0800
Subject: [PATCH] Fixed transformAST.TypeName

In transformAST.TypeName, it is possible for ctx.children to be null. An example scenario is when the last argument of a function definition has a trailing comma.

The existing implementation assumes ctx.children has the property 'length', which causes an exception when ctx.children is null. This commit fixes this issue by adding an if statement.
---
 src/ASTBuilder.js | 32 +++++++++++++++++---------------
 1 file changed, 17 insertions(+), 15 deletions(-)

diff --git a/src/ASTBuilder.js b/src/ASTBuilder.js
index 7c26230..9ea4cef 100644
--- a/src/ASTBuilder.js
+++ b/src/ASTBuilder.js
@@ -272,23 +272,25 @@ const transformAST = {
   },
 
   TypeName(ctx) {
-    if (ctx.children.length > 2) {
-      let length = null
-      if (ctx.children.length === 4) {
-        length = this.visit(ctx.getChild(2))
-      }
+    if (ctx.children) {
+      if (ctx.children.length > 2) {
+        let length = null
+        if (ctx.children.length === 4) {
+          length = this.visit(ctx.getChild(2))
+        }
 
-      return {
-        type: 'ArrayTypeName',
-        baseTypeName: this.visit(ctx.typeName()),
-        length
+        return {
+          type: 'ArrayTypeName',
+          baseTypeName: this.visit(ctx.typeName()),
+          length
+        }
       }
-    }
-    if (ctx.children.length === 2) {
-      return {
-        type: 'ElementaryTypeName',
-        name: toText(ctx.getChild(0)),
-        stateMutability: toText(ctx.getChild(1))
+      if (ctx.children.length === 2) {
+        return {
+          type: 'ElementaryTypeName',
+          name: toText(ctx.getChild(0)),
+          stateMutability: toText(ctx.getChild(1))
+        }
       }
     }
     return this.visit(ctx.getChild(0))