Property "etra_rows" seems not to be working

[Hitchki]

I am using grister as follows and would expect to get an extra row - but that does not happen.
(With "extra row" I mean getting a second, empty row with no data in it - which I guess ultimatelly would mean that the height of the ul is increased by the the heigt of an extra row)

<div class="gridster">
<ul>
<li data-row="1" data-col="1" data-sizex="1" data-sizey="1"></li>
<li data-row="1" data-col="2" data-sizex="1" data-sizey="1"></li>
</ul>
</div>

$(".gridster ul").gridster({
widget_margins: [10, 10],
widget_base_dimensions: [wid_base_dim_x, 200],
min_cols: 1,
extra_rows: 1,
max_cols: nrOfCols,