Gone evil mobs

Skeletons, spiders, zombies and creepers do not appear at night.

What I expected to happen was...:
I was waiting the night to collect cobwebs, bones and gunpowder

What actually happened was...:
angry mobs have not appeared.

Steps to Reproduce:
1. Waited for night.
2. Leave on street.
3. Angry mobs have not been spawned.