@marmbrus True, this is a more complicated issue. The discussion here also seems related: https://github.com/Parquet/parquet-mr/issues/158

As also said in the discussion of that Parquet PR I think you can model an array with nullable elements as essentially an array of structs. That would be handled by the other array converter that can contain nested types.

But yeah, the problem is more general. I think it would help to a `nullable` bit inside `DataType` so it's at least clear when something can be null. Now it's only in `StructField`.