code: private Object getFirst(
                             DeleteStack    stack)
      {
          Object q = null;
          GBSNode n = leftMostChild(stack);
          if (n != null)
          {
              q = n.leftMostKey();
              _current1.setLocation(n, 0);
          }
          return q;
      }
docs: Return first key in the index in key order, if any.
  
  <p>This also sets the node and index in _current1 if a key
  is found.</p>
  
  @param stack The stack to use to record the traversal.
  
  @return The first key in the index in key order or null
  if the index is empty.