Hello, this is not a Bug! Today I was playing and one night there were no mobs and I was in difficulty Hard, and the next day behind my house there were trees without leaves, once I was building a house and at one time I heard footsteps and I'm sure that this is Herobrine. Please remove it from the game! Thanks in advance!
Herobrine has never existed in vanilla minecraft. Check the wiki for more info on that.