Fixes the issue ignoring nulls when copy from arrow array to flat vector (#316)

* null fix after copying data from array to duckdb chunk

* add test to cover null cases

Author: y-f-u

src/vtab/arrow.rs

@@ -257,6 +257,13 @@ pub fn record_batch_to_duckdb_data_chunk(
 fn primitive_array_to_flat_vector<T: ArrowPrimitiveType>(array: &PrimitiveArray<T>, out_vector: &mut FlatVector) {
     // assert!(array.len() <= out_vector.capacity());
     out_vector.copy::<T::Native>(array.values());
+    if let Some(nulls) = array.nulls() {
+        for (i, null) in nulls.into_iter().enumerate() {
+            if !null {
+                out_vector.set_null(i);
+            }
+        }
+    }
 }
 
 fn primitive_array_to_flat_vector_cast<T: ArrowPrimitiveType>(
@@ -267,6 +274,13 @@ fn primitive_array_to_flat_vector_cast<T: ArrowPrimitiveType>(
     let array = arrow::compute::kernels::cast::cast(array, &data_type).unwrap();
     let out_vector: &mut FlatVector = out_vector.as_mut_any().downcast_mut().unwrap();
     out_vector.copy::<T::Native>(array.as_primitive::<T>().values());
+    if let Some(nulls) = array.nulls() {
+        for (i, null) in nulls.iter().enumerate() {
+            if !null {
+                out_vector.set_null(i);
+            }
+        }
+    }
 }
 
 fn primitive_array_to_vector(array: &dyn Array, out: &mut dyn Vector) -> Result<(), Box<dyn std::error::Error>> {
@@ -655,7 +669,7 @@ mod test {
         db.register_table_function::<ArrowVTab>("arrow")?;
 
         // Roundtrip a record batch from Rust to DuckDB and back to Rust
-        let schema = Schema::new(vec![Field::new("a", input_array.data_type().clone(), false)]);
+        let schema = Schema::new(vec![Field::new("a", input_array.data_type().clone(), true)]);
 
         let rb = RecordBatch::try_new(Arc::new(schema), vec![Arc::new(input_array.clone())])?;
         let param = arrow_recordbatch_to_query_params(rb);
@@ -746,6 +760,22 @@ mod test {
         Ok(())
     }
 
+    #[test]
+    fn test_primitive_roundtrip_contains_nulls() -> Result<(), Box<dyn Error>> {
+        let mut builder = arrow::array::PrimitiveBuilder::<arrow::datatypes::Int32Type>::new();
+        builder.append_value(1);
+        builder.append_null();
+        builder.append_value(3);
+        builder.append_null();
+        builder.append_null();
+        builder.append_value(6);
+        let array = builder.finish();
+
+        check_rust_primitive_array_roundtrip(array.clone(), array)?;
+
+        Ok(())
+    }
+
     #[test]
     fn test_timestamp_roundtrip() -> Result<(), Box<dyn Error>> {
         check_rust_primitive_array_roundtrip(Int32Array::from(vec![1, 2, 3]), Int32Array::from(vec![1, 2, 3]))?;