code: public String getString(String key, String defaultValue) {
          return this.props.getValueOrDefault(key, defaultValue);
      }
docs: Retrieves a configuration value with the given key
  
  @param key The key of the configuration value (e.g. application.name)
  @param defaultValue The default value to return of no key is found
  @return The configured value as String or the passed defautlValue if the key is not configured