Modernize codebase by replacing NULL with nullptr

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

Test: m
Bug: 68236239
Change-Id: I5b4123bc6709641315120a191e36cc57541349b2
diff --git a/tests/sys_msg_test.cpp b/tests/sys_msg_test.cpp
index 05ad01b..4eb5a14 100644
--- a/tests/sys_msg_test.cpp
+++ b/tests/sys_msg_test.cpp
@@ -71,7 +71,7 @@
   ASSERT_STREQ("hello world", msg.data);
 
   // Destroy the queue.
-  ASSERT_EQ(0, msgctl(id, IPC_RMID, 0));
+  ASSERT_EQ(0, msgctl(id, IPC_RMID, nullptr));
 }
 
 TEST(sys_msg, msgctl_failure) {