How set validation on size of string = 0 or min=5, max=10?
<p>I need set validation on input of String field. This field should be an empty or between <code>5</code> to <code>10</code> characters. But if I set validation like this:</p>

<pre><code>@Size(min=5, max=10)
private String couponCode;
</code></pre>

<p>It won't pass <code>@Valid</code> when the value is empty. How can I achieve that?</p>