Parent cannot be set for Coordinate element using createObject() method

import "script.js" as Scr

Rectangle {
         id: parentRect
}

Component{
         id: coordComponent
         Coordinate{}
         }

Component{
         id: polyLineComponent
         MapPolyline {}
         }

Component.onCompleted: {
      Scr.setCoordChild(coordComponent,polyLineComponent,parentRect)
}

.pragma library

function setCoordChild(coordElement,polyLineElement,pRect){

  var polyLineObj=polyLineElement.createObject(pRect);

  console.log("polyline parent :"+polyLineObj.parent); ====> Gives QDeclarativeRectangle_QML_1  

a)  var coordObj=coordElement.createObject(polyLineObj);

    console.log("coord obj :"+coordObj.parent); ====> Gives undefined 

b)  var coordObj1=coordElement.createObject(null);

    coordObj1.parent = polyLineObj;

    console.log("coord obj :"+coordObj.parent); ====> Gives undefined 

}