Modernize codebase by replacing NULL with nullptr

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

Test: m
Bug: 68236239
Change-Id: Id869744db54b5b366454a5e13b467ac1f4df2845
diff --git a/openjdkjvmti/ti_timers.cc b/openjdkjvmti/ti_timers.cc
index 24fb041..11b58c4 100644
--- a/openjdkjvmti/ti_timers.cc
+++ b/openjdkjvmti/ti_timers.cc
@@ -83,7 +83,7 @@
   // No CLOCK_MONOTONIC support on older Mac OS.
   struct timeval t;
   t.tv_sec = t.tv_usec = 0;
-  gettimeofday(&t, NULL);
+  gettimeofday(&t, nullptr);
   *nanos_ptr = static_cast<jlong>(t.tv_sec)*1000000000LL + static_cast<jlong>(t.tv_usec)*1000LL;
 #endif