fix fields param

Controllers/ExportController.php

@@ -84,7 +84,7 @@ class ExportController extends ControllerBase
 
         $request= $this->request->getJsonRawBody();
         $layerName = $request->layer;
-        $fields = $request->fields;
+        $fields = implode($request->fields, ',');
         $map = $request->map;
         $wfsRequest= $request->wfsRequest;
 
@@ -123,7 +123,7 @@ class ExportController extends ControllerBase
         if($oMap){
             if($oLayer = $oMap->getLayerByName($layerName)){
                 //TODO do it more safely getting info and not doing replace
-                $oLayer->setMetadata("gml_include_items",$fields);
+                $oLayer->setMetadata("gml_include_items", $fields);
             }
         }
         $oMap->save($tmp_mapfile_path);