code: private static String getPropertyValue(String key) {
          String env = System.getProperty(key);
          if (env == null) {
              if (DEFAULT_PROPS.containsKey(key)) {
                  return DEFAULT_PROPS.get(key);
              } else {
                  return null;
              }
          }
          return env;
      }
docs: Return a configured value, or the default.
  
  @param key
  @return If configured, return the system property value, else return a
  default. If a default is also not available, returns
  <code>null</code> if no default is configured.