Replace NULL macros with nullptr literals.

Change-Id: I918c40879aa547438f77e7d1a95fa2aa33bec398
diff --git a/cpp/rsCppInternal.h b/cpp/rsCppInternal.h
index ae43d47..81b690f 100644
--- a/cpp/rsCppInternal.h
+++ b/cpp/rsCppInternal.h
@@ -26,7 +26,7 @@
     }
 
 #define createDispatch(rs, dispatch) \
-    rs->getError() == RS_SUCCESS ? dispatch : NULL
+    rs->getError() == RS_SUCCESS ? dispatch : nullptr
 
 #undef LOG_TAG
 #undef LOG_NDEBUG