code: private static boolean getSystemProp(final String key, final boolean defaultValue) {
          String val = System.getProperty(key);
          if (val == null)
              val = System.getenv(key);
          if (val == null) {
              return defaultValue;
          } else if (val.isEmpty()) {
              return true;
          } else {
              switch (val.toLowerCase(Locale.ROOT)) {
                  case "t":
                  case "true":
                  case "1":
                      return true;
                  case "f":
                  case "false":
                  case "0":
                      return false;
                  default:
                      throw new IllegalArgumentException("Invalid value, expected true/false: " + val);
              }
          }
      }
docs: an error rather than return false. The default can also be specified.