title: error using container-filter in ComboBox field
body: <p>Using vaadin 7. Trying to do filtering. There is the error:
  vaadin.data.util.filter.generator.exception.MissingRequiredAttributeException: Required attribute value is null or missing.</p>
  <p>There is the filter:</p>
  <pre><code>&lt;container-filter&gt;
      &lt;if testExpr=&quot;not editNew or currentFacilityTreeIndexProperty.getValue() != null&quot;&gt;
          &lt;not&gt;
              &lt;like property=&quot;facilityTreeIndex&quot; valueExpr=&quot;currentFacilityTreeIndexProperty.getValue()&quot;
                                          onlyMatchPrefix=&quot;true&quot; /&gt;
          &lt;/not&gt;
      &lt;/if&gt;
  &lt;/container-filter&gt;
  </code></pre>
  <p>What is an attribute of a filter and what is missing? Other filters used in the same file for other ComboBoxFields have no attributes(if i get it right what attributes are):
  <code>&lt;container-filter&gt;</code></p>