Describe the bug

~700 sqllogictest cases are failing in Substrait round-trip mode because of the following error:

query failed: DataFusion error: Internal error: Null cast is not valid.

To Reproduce

cargo test --test sqllogictests -- --substrait-round-trip aggregate_skip_partial.slt:194

Expected behavior

The sqllogictest passes in Substrait round-trip mode

Additional context

This is part of a broader initiative to improve the reliability of Substrait-to-DataFusion logical plan conversions.

• [Epic] A collection of Substrait conversion issues #16248