Modernize codebase by replacing NULL with nullptr

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

Test: m
Bug: 68236239
Change-Id: Id869744db54b5b366454a5e13b467ac1f4df2845
diff --git a/tools/jfuzz/jfuzz.cc b/tools/jfuzz/jfuzz.cc
index 60c6275..a97a99c 100644
--- a/tools/jfuzz/jfuzz.cc
+++ b/tools/jfuzz/jfuzz.cc
@@ -1302,7 +1302,7 @@
 int32_t main(int32_t argc, char** argv) {
   // Time-based seed.
   struct timeval tp;
-  gettimeofday(&tp, NULL);
+  gettimeofday(&tp, nullptr);
 
   // Defaults.
   uint32_t seed = (tp.tv_sec * 1000000 + tp.tv_usec);