This is my DS also - he is now 7, and it seems that he just stopped wetting at night. The Dr. did say it is common in boys and it could be generic - my DH family had this problem.

I think I stopped the pull ups at 6 with an accident every now and then. I stopped before that with pull ups and we didn't have a problem but then he was wetting again, but then stopped. We also gave no drinks after a certain time and woke him up at night, nothing worked.

Just like potty training him it just seemed to click one day. Good Luck -