[OpenLayers-Users] Declare a default externalGraphic

[Heidt, Christopher M.]

I assign an externalGraphic to each of my features.
There is the possibility that the graphic for any given feature my not
resolve.
As it is now this results in an invisible feature.

So my question is: how can I declare a default image to use as an
externalGraphic
should the url I supply to externalGraphic fail to resolve?