public static String BOOLEAN(String key) {
    return key;
  }
Registers the configuration key that expects a boolean value. We actually don't register a
validator, because {@link Configuration#getBoolean} doesn't throw an exception even if the
value is not a boolean. So this is only for documentation purposes.
@param key configuration key
@return the key
hbase-common/src/main/java/org/apache/hadoop/hbase/conf/ConfigKey.java