Error when reading Avro containing null in a string column

[nenorbot]

Describe the bug

When reading an Avro file which contains a nullable string column with actual null values, this error occurrs:

ArrowError(SchemaError("expected resolvable string : GetString(Null)"))

To Reproduce

I have created a small repo which demonstrates the bug at https://github.com/nenorbot/datafusion_avro_null_string_issue

Expected behavior

Nullable string Avro columns should be supported

Additional context

No response