default boolean preExists(ObserverContext<? extends RegionCoprocessorEnvironment> c, Get get,
    boolean exists) throws IOException {
    return exists;
  }
Called before the client tests for existence using a Get.
<p>
Call CoprocessorEnvironment#bypass to skip default actions. If 'bypass' is set, we skip out on
calling any subsequent chained coprocessors.
@param c      the environment provided by the region server
@param get    the Get request
@param exists the result returned by the region server
@return the value to return to the client if bypassing default processing
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/RegionObserver.java