code: @Override
  	public PropertyResolver build() {
  		if (resolver != null) {
  			return resolver;
  		}
  		Converter converter = buildConverter();
  		List<PropertyResolver> delegates = buildProperties(converter);
  		return new FirstExistingPropertiesResolver(delegates);
  	}
docs: Build the {@link PropertyResolver}:
  <ul>
  <li>If a custom resolver is defined, use it directly</li>
  <li>If no custom resolver, use the {@link JavaPropertiesResolver} with
  merged {@link Properties} and converter instance provided by
  {@link ConverterBuilder#build()}</li>
  </ul>