Fix exception throwing to support no detail message.

(The empty string as a detail message is distinct from a NULL detail message,
and is treated differently by Throwable.printStackTrace.)

Change-Id: I8c65deac9f18c5782dcf6e72e4c37e6dd4174fe9
diff --git a/src/java_lang_reflect_Constructor.cc b/src/java_lang_reflect_Constructor.cc
index 6cc8ea7..4d42450 100644
--- a/src/java_lang_reflect_Constructor.cc
+++ b/src/java_lang_reflect_Constructor.cc
@@ -35,7 +35,7 @@
 jobject Constructor_constructNative(JNIEnv* env, jobject javaMethod, jobjectArray javaArgs, jclass javaDeclaringClass, jobjectArray javaParams, jint, jboolean) {
   Class* c = Decode<Class*>(env, javaDeclaringClass);
   if (c->IsAbstract()) {
-    Thread::Current()->ThrowNewException("Ljava/lang/InstantiationException;",
+    Thread::Current()->ThrowNewExceptionF("Ljava/lang/InstantiationException;",
         "Can't instantiate abstract class %s", PrettyDescriptor(c->GetDescriptor()).c_str());
     return NULL;
   }