Replace all uses of NULL with nullptr

This was an automatic change made by clang-tidy.  It moves all uses of
NULL to nullptr, which are equivalent, but nullptr is prefered.

Tested:  Code compiles.

Signed-off-by: Ed Tanous <ed.tanous@intel.com>
Change-Id: I9526599b222693c9723a69934b599c7a5b5d1fbf
diff --git a/redfish-core/lib/cpudimm.hpp b/redfish-core/lib/cpudimm.hpp
index d8d4191..ce36a0b 100644
--- a/redfish-core/lib/cpudimm.hpp
+++ b/redfish-core/lib/cpudimm.hpp
@@ -71,8 +71,8 @@
 {
     BMCWEB_LOG_DEBUG << "Get CPU resources by interface.";
 
-    const bool *present = NULL;
-    const bool *functional = NULL;
+    const bool *present = nullptr;
+    const bool *functional = nullptr;
     for (const auto &interface : cpuInterfacesProperties)
     {
         for (const auto &property : interface.second)