Changes to be done in merged FZ-filter

[lepetersson]

• In the merged version of the filter there is an error in the data preparation step (in the [notebook]) (https://github.com/OpenSenseAction/pypwsqc/blob/main/docs/notebooks/merged_filters.ipynb)
´N = ds_pws.rainfall.sel(id=neighbor_ids).isnull().sum(dim="id")

isnull() should be notnull()...

[fninsiima]

This error was not corrected in read the docs

[cchwala]

Thanks @fninsiima for pointing out this issue. If you want, you can do a small PR to fix this. If not, we will soon rework the docs a bit and fix this along the way.

This might even already change with #46, which changes the notebook quite a bit.