@Override
  public void readFields(DataInput in) throws IOException {
    super.readFields(in);
    namespace = Bytes.toString(Bytes.readByteArray(in));
  }
check if given action is granted in given namespace.
@param namespace namespace's name
@param action    action to be checked
@return true if granted, false otherwise
hbase-client/src/main/java/org/apache/hadoop/hbase/security/access/NamespacePermission.java