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: I0e0749db217667d9c3f51f8fac6cb58e8915e8d2
Signed-off-by: Jayanth Othayoth <ojayanth@gmail.com>
diff --git a/writefrudata.cpp b/writefrudata.cpp
index 44117ae..a4d5509 100644
--- a/writefrudata.cpp
+++ b/writefrudata.cpp
@@ -44,7 +44,7 @@
  */
 int cleanupError(FILE* fruFilePointer, FruAreaVector& fruAreaVec)
 {
-    if (fruFilePointer != NULL)
+    if (fruFilePointer != nullptr)
     {
         std::fclose(fruFilePointer);
     }
@@ -653,7 +653,7 @@
     }
 
     FILE* fruFilePointer = std::fopen(fruFilename, "rb");
-    if (fruFilePointer == NULL)
+    if (fruFilePointer == nullptr)
     {
         log<level::ERR>("Unable to open FRU file",
                         entry("FILE=%s", fruFilename),
@@ -687,7 +687,7 @@
 
     // We are done reading.
     std::fclose(fruFilePointer);
-    fruFilePointer = NULL;
+    fruFilePointer = nullptr;
 
     rc = ipmiValidateCommonHeader(fruData.data(), dataLen);
     if (rc < 0)