Not blank image in export request when all layers are turn off

[PauPérez_Puigcerver]

Hi,

I made a HTML viewer with the API Javascript 2.0, with a TOC that can turn on/off layers for each service. The problem is when you turn off all layers in one service, this service visualize default layers, instead of a blank image. The request in the viewer, when not all layers are off:

http://server:8399/arcgis/rest/services/intranet/incendios/MapServer/export?dpi=96&transparent=true&...

and the request when all layers are turn off:

http://server:8399/arcgis/rest/services/intranet/incendios/MapServer/export?dpi=96&transparent=true&...

Does anyone known what's the problem?

Thanks,

Pau Pérez