fixes webpack#136

Author: sokra

lib/Parser.js

@@ -469,7 +469,8 @@ Parser.prototype.walkVariableDeclarators = function walkVariableDeclarators(decl
 
 Parser.prototype.walkExpressions = function walkExpressions(expressions) {
 	expressions.forEach(function(expression) {
-		this.walkExpression(expression);
+		if(expression)
+			this.walkExpression(expression);
 	}, this);
 }
 

test/browsertest/lib/index.web.js

@@ -240,6 +240,11 @@ describe("main", function() {
 				a.should.be.eql("a");
 			});
 		});
+		
+		it("should parse sparse arrays", function() { // issue #136
+			[,null].should.have.length(2);
+			[0,,,0].should.have.length(4);
+		});
 	});
 
 	describe("polyfilling", function() {