Throw instead of return nothing

Author: ph-kev

src/Grids/pointcloud.jl

@@ -38,9 +38,9 @@ local_geometry_type(::Type{PointCloudGrid{C, GG, LG}}) where {C, GG, LG} =
 ClimaComms.context(grid::PointCloudGrid) = grid.context
 ClimaComms.device(grid::PointCloudGrid) = ClimaComms.device(grid.context)
 
-# No topology — return nothing. Callers that need a topology (e.g. DSS) should
-# not be called on a PointCloudGrid.
-topology(::PointCloudGrid) = nothing
+topology(::PointCloudGrid) = error(
+    "PointCloudGrid has no topology",
+)
 
 local_geometry_data(grid::PointCloudGrid, ::Nothing) = grid.local_geometry