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/pldmtool/pldm_platform_cmd.cpp b/pldmtool/pldm_platform_cmd.cpp
index 0a96274..d2c1c7d 100644
--- a/pldmtool/pldm_platform_cmd.cpp
+++ b/pldmtool/pldm_platform_cmd.cpp
@@ -846,7 +846,7 @@
 
     void printPDRFruRecordSet(uint8_t* data, ordered_json& output)
     {
-        if (data == NULL)
+        if (data == nullptr)
         {
             return;
         }
@@ -874,7 +874,7 @@
             {PLDM_ENTITY_ASSOCIAION_LOGICAL, "Logical"},
         };
 
-        if (data == NULL)
+        if (data == nullptr)
         {
             return;
         }
@@ -1495,7 +1495,7 @@
     void printPDRMsg(uint32_t& nextRecordHndl, const uint16_t respCnt,
                      uint8_t* data, std::optional<uint16_t> terminusHandle)
     {
-        if (data == NULL)
+        if (data == nullptr)
         {
             std::cerr << "Failed to get PDR message" << std::endl;
             return;