[OpenLayers-Users] Zoom to a Layer's Extent

[Bill Thoen]

I want to zoom a map to the extent of a layer (called baseLayer) but 
when I try:
map.zoomToExtent(baseLayer.getDataExtent());
the baseLayer.getDataExtent() function returns null. When I don't 
include this line everything works fine (the layer appears normally, 
only without the zoom that I want.) What am I missing here?