title: JSR Validation @Pattern allowing null values
body: <p>When I annotate a field with  @Pattern</p>
  <pre><code>@Pattern(regexp=&quot;someRegexp&quot;)
  public String name;
  </code></pre>
  <p>If the JSON contains this field, with value as <strong>null</strong>, then I expect this regex to fail and thus invalid.</p>
  <p>if the JSON does NOT contain this field, then it is fine for the validation to pass.</p>
  <p>How to achieve this?</p>