If an empty multi-expression somehow sneaks through to GenerateJavaScriptAST,
convert it to a JavaScript undefined.

Review by: scottb

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@2973 8db76d5a-ed1c-0410-87a9-c151d255dfc7

dev/core/src/com/google/gwt/dev/jjs/impl/GenerateJavaScriptAST.java

diff --git a/dev/core/src/com/google/gwt/dev/jjs/impl/GenerateJavaScriptAST.java b/dev/core/src/com/google/gwt/dev/jjs/impl/GenerateJavaScriptAST.java
index ec71c24..04942fb 100644
--- a/dev/core/src/com/google/gwt/dev/jjs/impl/GenerateJavaScriptAST.java
+++ b/dev/core/src/com/google/gwt/dev/jjs/impl/GenerateJavaScriptAST.java
@@ -917,6 +917,10 @@
         JsExpression next = exprs.get(i);
         cur = createCommaExpression(cur, next);
       }
+      if (cur == null) {
+        // the multi-expression was empty; use undefined
+        cur = jsProgram.getUndefinedLiteral();
+      }
       push(cur);
     }