The esri ascii import, in a mapset located in the catalog window seem to work
not properly with novalue as 0.0 or -9.0. Importing an esri ascii map with the
right clik on the mapset, JGrass ask for define the righ novalue. When the
novalue is 0.0 or -9.0 (I didn't try with other values) the map is displayed
as the indicated novalue is a normal value, not a null. If the novalue is
-9999.0 the novalue is right represented as a null value.