CommonDatamodel.parentdataset for root group for a multi-file should be nothing

Author: Alexander-Barth

src/dataset.jl

@@ -17,7 +17,14 @@ only a single group, this will be always the root group `"/"`.
 """
 name(ds::AbstractDataset) = "/"
 
+"""
+    pds = CommonDatamodel.parentdataset(ds::AbstractDataset)
+
+The data set `pds` containing `ds` as a sub-group.
+`pds` is nothing for the root group.
+"""
 parentdataset(ds::AbstractDataset) = nothing
+
 sync(ds::AbstractDataset) = nothing
 
 """

src/multifile.jl

@@ -62,7 +62,12 @@ end
 
 function parentdataset(mfds::MFDataset)
     ds = parentdataset.(mfds.ds)
-    return MFDataset(ds,mfds.aggdim,mfds.isnewdim,mfds.constvars)
+
+    if isnothing(ds[1])
+        return nothing
+    else
+        return MFDataset(ds,mfds.aggdim,mfds.isnewdim,mfds.constvars)
+    end
 end
 
 Base.Array(v::MFVariable) = Array(v.var)