Reads the hillshade OVERLAY a basemap declares, if it declares one that can be drawn.
null without a word when the basemap asks for none: no hillshade.overlay, or a basemap of
type: "hillshade", whose shading is the basemap itself. null with an error logged when it
asks for one without a usable demUrl.
Reads the hillshade OVERLAY a basemap declares, if it declares one that can be drawn.
nullwithout a word when the basemap asks for none: nohillshade.overlay, or a basemap oftype: "hillshade", whose shading is the basemap itself.nullwith an error logged when it asks for one without a usabledemUrl.