Add check for nil nativeToJS bridge

Reviewed By: mhorowitz

Differential Revision: D3980922

fbshipit-source-id: ba8ba283cd186a28cd9d5c1c35d4828829864a6a

ReactCommon/cxxreact/Instance.h

@@ -58,6 +58,7 @@ class Instance {
   // This method is experimental, and may be modified or removed.
   template <typename T>
   Value callFunctionSync(const std::string& module, const std::string& method, T&& args) {
+    CHECK(nativeToJsBridge_);
     return nativeToJsBridge_->callFunctionSync(module, method, std::forward<T>(args));
   }