Bug Report: Column Nullability Not Honored in FlightSqlProducer Schema

从 org.apache.arrow.driver.jdbc.utils.ConvertUtils.convertArrowFieldsToColumnMetaDataList() 开始，该方法会将 Arrow Field 对象转换为 Flight SQL 驱动程序的 ColumnMetaData 实例。检查 ColumnMetaData.Builder 的填充方式，并验证生成的元数据是否保留每个字段的 nullability。nullable 和 non-nullable 的 Arrow 字段能够公开匹配的 ResultSetMetaData 值即表示完成。

Describe the bug, including details regarding any error messages, version, and platform.

In the FlightSqlProducer class, the getFlightInfoPreparedStatement method is responsible for returning the Arrow Schema of the ResultSet for a given query. However, the returned schema does not accurately reflect the nullability of columns. Regardless of whether a column is defined as nullable or non-nullable, the schema always returns a fixed nullability value.

This leads to incorrect ResultSetMetaData when the schema is consumed via the Flight SQL driver.

Root Cause:

The issue originates in the method:

org.apache.arrow.driver.jdbc.utils.ConvertUtils.convertArrowFieldsToColumnMetaDataList()

Here, a list of org.apache.arrow.vector.types.pojo.Field objects is converted into org.apache.calcite.avatica.ColumnMetaData instances. However, the setNullable property of the ColumnMetaData.Builder is not being set based on the actual nullability of the Arrow field.

Expected Behavior:

The setNullable method of ColumnMetaData.Builder should be updated to reflect the value of field.isNullable() from the Arrow schema.

Impact:

This bug results in incorrect metadata being exposed to clients using the Flight SQL driver, potentially leading to misinterpretation of the data schema.