use assert and compare None with `is`
use assert and compare None with `is`

chainer/chainer,ktnyt/chainer,ktnyt/chainer,okuta/chainer,hvy/chainer,niboshi/chainer,okuta/chainer,keisuke-umezawa/chainer,hvy/chainer,niboshi/chainer,okuta/chainer,chainer/chainer,pfnet/chainer,keisuke-umezawa/chainer,hvy/chainer,niboshi/chainer,wkentaro/chainer,keisuke-umezawa/chainer,tkerola/chainer,wkentaro/chainer,anaruse/chainer,jnishi/chainer,chainer/chainer,jnishi/chainer,wkentaro/chainer,ronekko/chainer,keisuke-umezawa/chainer,niboshi/chainer,okuta/chainer,wkentaro/chainer,ktnyt/chainer,chainer/chainer,rezoo/chainer,hvy/chainer,jnishi/chainer,jnishi/chainer,ktnyt/chainer