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_epoll_test.cpp b/tests/sys_epoll_test.cpp
index 7233ccc..18cf380 100644
--- a/tests/sys_epoll_test.cpp
+++ b/tests/sys_epoll_test.cpp
@@ -33,11 +33,11 @@
   ASSERT_EQ(0, epoll_wait(epoll_fd, events, 1, 1));
 
   // epoll_pwait without a sigset (which is equivalent to epoll_wait).
-  ASSERT_EQ(0, epoll_pwait(epoll_fd, events, 1, 1, NULL));
+  ASSERT_EQ(0, epoll_pwait(epoll_fd, events, 1, 1, nullptr));
 
 #if defined(__BIONIC__)
   // epoll_pwait64 without a sigset (which is equivalent to epoll_wait).
-  ASSERT_EQ(0, epoll_pwait64(epoll_fd, events, 1, 1, NULL));
+  ASSERT_EQ(0, epoll_pwait64(epoll_fd, events, 1, 1, nullptr));
 #endif
 
   // epoll_pwait with a sigset.