Check for callback argument in PTR lookup

src/node_dns.cc

@@ -443,6 +443,11 @@ static Handle<Value> Reverse(const Arguments& args) {
           String::New("Argument must be a string.")));
   }
 
+  if (!args[1]->IsFunction()) {
+    return ThrowException(Exception::Error(
+          String::New("Missing callback argument")));
+  }
+
   String::Utf8Value ip_address(args[0]->ToString());
 
   union {

test/disabled/test-dns.js

@@ -8,7 +8,10 @@ var dns = require("dns"),
 
 assert.throws(function () {
   dns.resolve('google.com', 'A');
-})
+});
+assert.throws(function () {
+  dns.resolve('127.0.0.1', 'PTR');
+});
 
 
 var hosts = ['example.com', 'example.org',