[example] ignore clip_gradient if not set
[example] ignore clip_gradient if not set

sxjscience/mxnet,sxjscience/mxnet,sxjscience/mxnet,sxjscience/mxnet,sxjscience/mxnet,sxjscience/mxnet,sxjscience/mxnet,sxjscience/mxnet,sxjscience/mxnet