use nullptr in Hybrid.h (facebook#29)

Summary:
## Motivation

Why are you making this change?

What did you change?

How does the code work?

Why did you choose this approach?
Pull Request resolved: facebookincubator/fbjni#29

Test Plan:
How did you test this change?
Any change that adds functionality should add a unit test as well.

Reviewed By: mhorowitz

Differential Revision: D19347378

Pulled By: passy

fbshipit-source-id: 4022289d222e507d82ce601239719b899e40867c

first-party/fbjni/cxx/fbjni/detail/Hybrid.h

@@ -319,7 +319,7 @@ inline detail::BaseHybridClass* getHybridDataFromField(const JObject* self, cons
 
 template <typename T, typename B>
 inline T* HybridClass<T, B>::JavaPart::cthis() const {
-  detail::BaseHybridClass* result = 0;
+  detail::BaseHybridClass* result = nullptr;
   static const auto hybridDataField = detectHybrid<T, B>(this->getClass());
   const bool isHybrid = !hybridDataField;
   if (isHybrid) {