clang-tidy: Replace NULL with nullptr

Replaced all instances of NULL with nullptr to improve type safety
and clarity, as nullptr is the modern C++ standard for null pointers.

Tested: Build verified

Change-Id: If9e6c34c48821a7cf8577a2166727ce7db06fadc
Signed-off-by: Jayanth Othayoth <ojayanth@gmail.com>
diff --git a/libpldmresponder/platform_state_sensor.hpp b/libpldmresponder/platform_state_sensor.hpp
index 20973b9..003763f 100644
--- a/libpldmresponder/platform_state_sensor.hpp
+++ b/libpldmresponder/platform_state_sensor.hpp
@@ -110,7 +110,7 @@
     while (pdrRecord)
     {
         pdr = reinterpret_cast<pldm_state_sensor_pdr*>(pdrEntry.data);
-        assert(pdr != NULL);
+        assert(pdr != nullptr);
         if (pdr->sensor_id != sensorId)
         {
             pdr = nullptr;