clang-tidy: Enable modernize-use-nullptr

Modified code to address issues flagged by this check.

Tested: Build and unit tests passed successfully.

Change-Id: I25f984d06a2dbdeb65d64fe8f90929b2af1ea796
Signed-off-by: Jayanth Othayoth <ojayanth@gmail.com>
diff --git a/test/debug_inif_test.cpp b/test/debug_inif_test.cpp
index 08cb2a7..59472ef 100644
--- a/test/debug_inif_test.cpp
+++ b/test/debug_inif_test.cpp
@@ -23,7 +23,7 @@
         std::span<char> tmpdirSpan(reinterpret_cast<char*>(tmpdir),
                                    sizeof(tmpdir));
         auto dirPtr = mkdtemp(tmpdirSpan.data());
-        if (dirPtr == NULL)
+        if (dirPtr == nullptr)
         {
             throw std::bad_alloc();
         }