Replace NULL with nullptr

Also fixed some lines that were too long, and a few other minor
details.

Change-Id: I6efba5fb6e03eb5d0a300fddb2a75bf8e2f175cb
diff --git a/runtime/art_field.h b/runtime/art_field.h
index 16c46f0..c0620bf 100644
--- a/runtime/art_field.h
+++ b/runtime/art_field.h
@@ -158,7 +158,7 @@
     return (GetAccessFlags() & kAccVolatile) != 0;
   }
 
-  // Returns an instance field with this offset in the given class or nullptr if not found.
+  // Returns an instance field with this offset in the given class or null if not found.
   static ArtField* FindInstanceFieldWithOffset(mirror::Class* klass, uint32_t field_offset)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);