Modernize codebase by replacing NULL with nullptr

Fixes -Wzero-as-null-pointer-constant warning.

Test: m
Bug: 68236239
Change-Id: I226a0599db4f7c3557e55cade7869d00bd314949
diff --git a/server/ndc.cpp b/server/ndc.cpp
index c86e53e..836e802 100644
--- a/server/ndc.cpp
+++ b/server/ndc.cpp
@@ -76,7 +76,7 @@
     } else {
         final_cmd = strdup("");
     }
-    if (final_cmd == NULL) {
+    if (final_cmd == nullptr) {
         int res = errno;
         perror("strdup failed");
         return res;