r.fillnulls: Input map has no holes || No NULL cells found

[zarch]

I'm trying to use r.fillnuls to fill a CELL map [0] with four categories.

G70> g.region rast=tree_rm_small -p  # set the region
projection: 99 (Transverse Mercator)
zone:       0
datum:      osgb36
ellipsoid:  airy
north:      673614.75
south:      672309.75
west:       324718.25
east:       326676
nsres:      0.25
ewres:      0.25
rows:       5220
cols:       7831
cells:      40877820

G70> r.stats -c -l input=tree_rm_small  # check that the map has NULLs
 100%
1  7612219
2  10576095
3  10678651
4  7654913
* no data 4355942

But I got:

G70> r.fillnulls input=tree_rm_small output=tree_rm_small__fill
 100%
 100%
ERROR: Input map has no holes. Check region settings.
G70> r.fillnulls input=tree_rm_small output=tree_rm_small__fill method=linear
 100%
 100%
ERROR: No NULL cells found in input raster.

How can I solve it? Any hints?

[zarch]

raster map to fill with r.fillnulls

[marisn]

As fillnulls is using spline interpolator to fill NULL areas, it wouldn't make any sense for category data as You seem to have (i.e. what is category 3.67?). I would rather tend to fix r.fillnulls to not accept CELL map type to prevent users from filling holes in categorized data sets.

[marisn]

I could not reproduce the issue with 7.3 on Linux with provided data or with my own data.* If the problem still persists, a location with sample data should be provided for testing.

.* Of course, output of r.fillnulls on CELL data is FCELL/DCELL