[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

首先重现报告的从 nullable Avro schema 到 nullable Arrow schema 的转换，然后将其写入 Parquet 文件并捕获 sparse_union 失败。确认转换路径是否支持此 schema，并记录预期行为或限制；issue 中未确定源文件或测试。

由索引模型根据 Issue 内容生成。