Map data should be a non-nullable struct type

[tanejagagan]

Getting exception while trying to access map data type
java.lang.IllegalArgumentException: Map data should be a non-nullable struct type

at org.apache.arrow.util.Preconditions.checkArgument(Preconditions.java:126)
at org.apache.arrow.vector.complex.MapVector.initializeChildrenFromFields(MapVector.java:96)
at org.apache.arrow.vector.types.pojo.Field.createVector(Field.java:107)
at org.apache.arrow.vector.ipc.ArrowReader.initialize(ArrowReader.java:187)
at org.apache.arrow.vector.ipc.ArrowReader.ensureInitialized(ArrowReader.java:171)
at org.apache.arrow.vector.ipc.ArrowReader.getVectorSchemaRoot(ArrowReader.java:68)
at org.apache.arrow.c.ArrowArrayStreamReader.loadNextBatch(ArrowArrayStreamReader.java:68)
at io.dazzleduck.spark.MapTypeTest.testMapType(MapTypeTest.java:28)
at java.base/java.lang.reflect.Method.invoke(Method.java:580)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)

import org.apache.arrow.memory.RootAllocator;
import org.apache.arrow.vector.ipc.ArrowReader;
import org.duckdb.DuckDBConnection;
import org.duckdb.DuckDBResultSet;
import org.junit.jupiter.api.Test;

import java.io.IOException;
import java.sql.DriverManager;
import java.sql.SQLException;

public class MapTypeTest {
    @Test
    void testMapType() throws SQLException, IOException {
        var selectStatement = "select map { 'k1' : 'v1' } as m";
        DuckDBConnection connection = (DuckDBConnection) DriverManager.getConnection("jdbc:duckdb:");
        try (var s = connection.createStatement()) {
            s.execute(selectStatement);
            try(var resultSet = (DuckDBResultSet)s.getResultSet();
                var allocator = new RootAllocator()) {
                    try (var reader = (ArrowReader) resultSet.arrowExportStream(allocator, 256)) {
                        while (reader.loadNextBatch()) {
                            System.out.println(reader.getVectorSchemaRoot().contentToTSVString());
                        }
                    }
            }
        }
    }
}