code: private static void setConfigurationFromSystemProperty(Configuration configuration,
        String propertyName) {
      String propertyValue = System.getProperty(propertyName);
      if (propertyValue != null && configuration.get(propertyName) == null) {
        configuration.set(propertyName, propertyValue);
      }
    }
docs: Set the System property into Hadoop configuration.
  
  This method won't override existing property even if it is set as System property.
  
  @param configuration Hadoop configuration
  @param propertyName the property to be set