It is a bug in `MiniDFSCluster`, reference [here](http://stackoverflow.com/questions/17625938/hbase-minidfscluster-java-fails-in-certain-environments). MiniDFSCluster creates fake HDFS in your local disk when doing test. But if it encounters the improper `umask` in Linux system, it would complain about NPE, which took me lots of time to find the reason and fixed it.