Modernize codebase by replacing NULL with nullptr

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

Test: m
Bug: 68236239
Change-Id: I8cb04f9f99be029d7fef13c4c7c77aea515f3d61
diff --git a/minijail/HardwareMinijail.cpp b/minijail/HardwareMinijail.cpp
index e6b1144..990a689 100644
--- a/minijail/HardwareMinijail.cpp
+++ b/minijail/HardwareMinijail.cpp
@@ -29,7 +29,7 @@
     }
 
     struct minijail* jail = minijail_new();
-    if (jail == NULL) {
+    if (jail == nullptr) {
         LOG(FATAL) << "Failed to create minijail.";
     }