hi: How to deal with <http://www.baidu.com/link?url=gXuNJjK_D8dbqNxLwXQO4KfU9lIUyyE6Cyt54hx68EVKcnohBk0ZyRbBAje7p4Kgt7h34FGpwk8YEnqAVspGw4iP0esmMTaUPkVfdaqsRNi> null value here?
https://github.com/apache/incubator-hivemall/blob/master/core/src/main/java/hivemall/ftvec/scaling/RescaleUDF.java#L81
