clang-tidy: Enable modernize-use-nullptr check

This check converts the usage of null pointer constants
(e.g. NULL, 0) to use the new C++11 and C23 nullptr keyword.

Signed-off-by: George Liu <liuxiwei@ieisystem.com>
Change-Id: I10dccfd0513385c583ca07d13ed71edb04b58853
diff --git a/manager/lamptest/lamptest.cpp b/manager/lamptest/lamptest.cpp
index 3ae6d36..6f24973 100644
--- a/manager/lamptest/lamptest.cpp
+++ b/manager/lamptest/lamptest.cpp
@@ -251,7 +251,7 @@
 
 bool LampTest::requestHandler(Group* group, bool value)
 {
-    if (groupObj == NULL)
+    if (groupObj == nullptr)
     {
         groupObj = std::move(group);
     }