code: private Properties loadPropertiesFile() throws IOException {
      Properties props = new Properties();
      File propsFile;
      if (propertiesFile != null) {
        propsFile = new File(propertiesFile);
        checkArgument(propsFile.isFile(), "Invalid properties file '%s'.", propertiesFile);
      } else {
        propsFile = new File(getConfDir(), DEFAULT_PROPERTIES_FILE);
      }
  
      if (propsFile.isFile()) {
        try (InputStreamReader isr = new InputStreamReader(
            new FileInputStream(propsFile), StandardCharsets.UTF_8)) {
          props.load(isr);
          for (Map.Entry<Object, Object> e : props.entrySet()) {
            e.setValue(e.getValue().toString().trim());
          }
        }
      }
      return props;
    }
docs: Loads the configuration file for the application, if it exists. This is either the
  user-specified properties file, or the spark-defaults.conf file under the Spark configuration
  directory.