Added handling of empty handles to String::AsciiValue and String::Value.

src/api.cc

Index: src/api.cc
===================================================================
--- src/api.cc	(revision 538)
+++ src/api.cc	(working copy)
@@ -2649,6 +2649,11 @@
 
 String::AsciiValue::AsciiValue(v8::Handle<v8::Value> obj) {
   EnsureInitialized("v8::String::AsciiValue::AsciiValue()");
+  if (obj.IsEmpty()) {
+    str_ = NULL;
+    length_ = 0;
+    return;
+  }
   HandleScope scope;
   TryCatch try_catch;
   Handle<String> str = obj->ToString();
@@ -2670,6 +2675,11 @@
 
 String::Value::Value(v8::Handle<v8::Value> obj) {
   EnsureInitialized("v8::String::Value::Value()");
+  if (obj.IsEmpty()) {
+    str_ = NULL;
+    length_ = 0;
+    return;
+  }
   HandleScope scope;
   TryCatch try_catch;
   Handle<String> str = obj->ToString();