post XML查询wfs的问题

var pa=" <Filter> <PropertyIsLike> <PropertyName>bl_id </PropertyName> <Literal>$('#txt').val()+‘*’ </Literal> </PropertyIsLike> </Filter>";
  $.ajax({
  type: "POST",
  dataType:"html",
  url: "http://jcdesktop/cgi-bin/mapserv?map=/map/projects/hku/floorplan.map&SERVICE=WFS&VERSION=1.0.0&REQUEST=getfeature&typename=room",
  processData:false,
  data:"filter="+pa,
  success: function(xml){  
  $("#getfea").html(xml);
  }
});
  $('#txt').val("");

在文本框里面输入，点按钮执行上面代码  返回下面
<wfs:FeatureCollection xsi:schemaLocation="http://www.opengis.net/wfs http://schemas.opengeospatial.net//wfs/1.0.0/WFS-basic.xsd                        http://mapserver.gis.umn.edu/mapserver http://192.168.0.22/cgi-bin/mapserv?map=/map/projects/hku/floorplan.map&SERVICE=WFS&VERSION=1.0.0&REQUEST=DescribeFeatureType&TYPENAME=room&OUTPUTFORMAT=XMLSCHEMA">
−
<gml:boundedBy>
<gml:null>missing </gml:null>
</gml:boundedBy>
</wfs:FeatureCollection>
帮忙看看那里出错了。。怎么没返回数据