libgis: G_OPT_M_NULL_VALUE cosmetics

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@63017 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/gis/parser_standard_options.c

@@ -672,7 +672,7 @@ struct Option *G_define_standard_option(int opt)
         Opt->type = TYPE_STRING;
         Opt->required = NO;
         Opt->multiple = NO;
-        Opt->description = _("String representing NULL value data cell");
+        Opt->description = _("String representing NULL value");
         break;
         
     case G_OPT_M_REGION: