code: public static String getSystemProperty(String key, @Nullable String defaultValue) {
      String value;
      try {
        value = System.getProperty(key);
      } catch (AccessControlException ex) {
        return defaultValue;
      }
      return value != null ? value : defaultValue;
    }
docs: Returns the system property, or {@code defaultValue} if the system property is null or
  cannot be read (e.g. because of security policy restrictions).