Response to WFS query on a sql view returns zero for the number of features

The response to a WFS query on a sql view returns zero for the number of features

/geoserver/ows?service=WFS&version=1.0.0&request=GetFeature&typeName=myns:test_sql_view&maxFeatures=50&outputFormat=GML2

returns

<wfs:FeatureCollection numberOfFeatures="0" ...>
<gml:featureMembers>
<gml:boundedBy/>
<myns:test_sql_view gml:id="test_sql_view.fid-7b81134_12ca359e616_db5"/>
<myns:test_sql_view gml:id="test_sql_view.fid-7b81134_12ca359e616_db6"/>
..
<gml:featureMembers>
</wfs:FeatureCollection>