docs: protected Properties difference(final Map map) {
          final Properties difference = new Properties();
          for (final Object o : map.entrySet()) {
              final Map.Entry entry = (Map.Entry) o;
              final String key = (String) entry.getKey();
              final String val = (String) entry.getValue();
              if (!properties.containsKey(key)) {
                  difference.setProperty(key, val);
              }
          }
          return difference;
      }