title: Empty optional element error?
body: <p>I have an element, <code>labels</code>, whose <code>minoccurs="0"</code> and <code>minLength="1"</code>. </p>
  
  <pre><code>&lt;xs:element name="labels" type="x2x:labels" minOccurs="0" /&gt;
  
  &lt;xs:simpleType name="labels"&gt;
          &lt;xs:restriction&gt; 
              &lt;xs:simpleType&gt; 
                  &lt;xs:list itemType="xs:token" /&gt;
              &lt;/xs:simpleType&gt;    
              &lt;xs:minLength value="1" /&gt; 
          &lt;/xs:restriction&gt; 
      &lt;/xs:simpleType&gt;
  </code></pre>
  
  <p>When the <code>labels</code> is not set I get the following error:</p>
  
  <blockquote>
    <p>Caused by: org.xml.sax.SAXParseException; lineNumber: 0; columnNumber: 0; 
    cvc-minLength-valid: Value '' with length = '0' is not facet-valid with respect to minLength '1' for type 'labels'.</p>
  </blockquote>
  
  <p>As per my knowledge, if <code>minOccurs=0</code> and I am not setting the element, it should not given any error as it's meant to be optional.</p>