Avoid NullPointerException When users do not indicate io.compression.codecs option. #25
Description
When io.compression.codecs option does not exist in users' configuration of hdfs( config_files option and config option), this plugin throws NullPointerException. When NullPointerException is thrown, users cannot know the cause is io.compression.codecs option. Therefore, this should throw ConfigException when io.compression.codecs option does not exist.