[Java] nullable arrow schema write to parquet error

### Describe the usage question you have. Please include as many useful details as possible.

When I convert nullable avro schema to nullable arrow schema and write as parquet file， meet a exception

"Unhandled type for Arrow to Parquet schema conversion: sparse_union"

It seems arrow-avro not support SPARE_UNION

how can I use nullable schema in arrow, please help me.

### Component(s)

Java

首先重現回報的從 nullable Avro schema 到 nullable Arrow schema 的轉換，然後將其寫入 Parquet 檔案並擷取 sparse_union 失敗。確認轉換路徑是否支援此 schema，並記錄預期行為或限制；issue 中未識別出原始碼檔案或測試。

由索引模型根據 Issue 內容生成。