WFS Filter PropertyName lost

Using the following WFS-Filter we want to reduce the response from the WFS to the attributes 'ogc_fid' and 'cat'. It works properly with geoserver.

```

ogc_fid
cat


sensing_time

2013-02-02T13:00:00.000Z


2017-01-03T15:20:47.654Z

```
Converting this XML to JSON with JSONIX produces the following result:

```
{
"name": {
"namespaceURI": "http://www.opengis.net/wfs/2.0",
"localPart": "GetFeature",
"prefix": "wfs",
"key": "{http://www.opengis.net/wfs/2.0}GetFeature",
"string": "{http://www.opengis.net/wfs/2.0}wfs:GetFeature"
},
"value": {
"TYPE_NAME": "WFS_2_0.GetFeatureType",
"service": "WFS",
"version": "2.0.0",
"startIndex": 0,
"count": 25,
"outputFormat": "application/json",
"abstractQueryExpression": [{
"name": {
"namespaceURI": "http://www.opengis.net/wfs/2.0",
"localPart": "Query",
"prefix": "wfs",
"key": "{http://www.opengis.net/wfs/2.0}Query",
"string": "{http://www.opengis.net/wfs/2.0}wfs:Query"
},
"value": {
"TYPE_NAME": "WFS_2_0.QueryType",
"typeNames": ["EOME:WRS2"],
"abstractSortingClause": {
"name": {
"namespaceURI": "http://www.opengis.net/wfs/2.0",
"localPart": "PropertyName",
"prefix": "wfs",
"key": "{http://www.opengis.net/wfs/2.0}PropertyName",
"string": "{http://www.opengis.net/wfs/2.0}wfs:PropertyName"
},
"value": {
"TYPE_NAME": "WFS_2_0.PropertyName",
"value": {
"namespaceURI": "",
"localPart": "cat",
"prefix": "",
"key": "cat",
"string": "cat"
}
}
}
}
}]
}
}
```

It seems that only the last PropertyName ('cat') has been considered. The PropertyName 'ogc_fid' has been ignored.
Vice versa we have the same problem to generate a json and convert it to XML with several PropertyNames so that the result-XML looks like the XML-example (see above).

Thank you and best regards