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/.clang-tidy b/.clang-tidy
index d1d47cd..116e43b 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -222,6 +222,7 @@
 modernize-use-equals-default,
 modernize-use-equals-delete,
 modernize-use-noexcept,
+modernize-use-nullptr,
 modernize-use-override,
 modernize-use-transparent-functors,
 modernize-use-uncaught-exceptions,
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);
     }
diff --git a/manager/lamptest/lamptest.hpp b/manager/lamptest/lamptest.hpp
index c7804c8..5e312e2 100644
--- a/manager/lamptest/lamptest.hpp
+++ b/manager/lamptest/lamptest.hpp
@@ -39,7 +39,7 @@
      */
     LampTest(const sdeventplus::Event& event, Manager& manager) :
         timer(event, [this](auto&) { timeOutHandler(); }), manager(manager),
-        groupObj(NULL)
+        groupObj(nullptr)
     {
         // Get the force update and/or skipped physical LEDs names from the
         // lamp-test-led-overrides.json file during lamp