Re: unchecked conversion warning.

This code compiles with an 'unchecked conversion' warning.
I have tried various corrections, for example casting like (Vector<Object>), but to no
avail.
What am I doing wrong?l
The code is the smallest demo I could make from the original application.

import java.util.Vector;
public class genericsdemo
{
   private static Vector<Vector> vdata = new Vector<Vector>(); //a Vector of Vectors

   private static Vector<Object> vrow = new Vector<Object>(); //a row

   public static void main(String args[]) {
     vrow.add(null); //two columns in the row
     vrow.add(null);

     vdata.add(vrow); //add the row to the Vector of Vectors

     Vector vtmp = getrow(); //test

   }

   private static Vector<Object> getrow() {
     return vdata.elementAt(0); //warning: [unchecked] unchecked conversion
   }
}