Describe the bug
r.fillnulls grass command reports "Input map has no holes" with rst method when I process a raster without NaN values.

To Reproduce
Steps to reproduce the behavior:

1. Load a raster without NaN values to any grass mapset.
2. start r.fillnulls command for this raster with defaults
3. See error "Input map has no holes"

Expected behavior
r.fillnulls should check for NaNs and copy the input map to desired location with desired name without changing it if it has no NaN values. I the g.region is smaller than the map, it should export to the output only the extent of this region of course.

System description (please complete the following information):

• Operating System: Linux Centos
• GRASS GIS version 8.2