I have three Ayam Cemani birds that were hatched this spring by a broody Bielefelder. She has hatched me a couple of dozen chicks over the last three years, and these are the only ones that have ever turned out to be so nervous, so I have to assume that it's the breed, and not the way they were raised.
However they are beautiful birds, with a calm (if very nervous) nature. I have two pullets and a rooster, who started to crow at 7 weeks old! He crowed half a dozen times over a couple of weeks, then stopped, and didn't start again until he was over 4 months old. At 6 months he has just started mounting the hens, and he is very gentle with them - not aggressive in any way. He is braver than his sisters, and will happily come and eat out of my hand, although I can only touch him when he is on the roost at night. His two sisters are very flighty - scared of their own shadows, and need a lot of persuading to even eat out of my hand.
*Edit* With age the two pullets have become much braver and less nervous. They both eat out of my hand without problem now, and are easier to pick up and handle. Interestingly they both decided to brood during their first winter - one in January and one in February, but have turned out to be wonderful chicken mums!
However their brother, despite being the alpha male in the flock, is still as nervous as ever, and backs away whenever I come near him. I doubt that will change, but he will stay with the flock as he is still gentle with his girls, and really beautiful!