default void preGetNamespaceDescriptor(ObserverContext<MasterCoprocessorEnvironment> ctx,
    String namespace) throws IOException {
  }
Called before a getNamespaceDescriptor request has been processed.
@param ctx       the environment to interact with the framework and master
@param namespace the name of the namespace
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/MasterObserver.java