From bc3ef33c47d9746be43e3a8de1e2d876c05007e8 Mon Sep 17 00:00:00 2001
From: "Jorge C. Leitao" <jorgecarleitao@gmail.com>
Date: Sun, 6 Dec 2020 06:54:06 +0100
Subject: [PATCH] Fixed error in MutableArrayData

---
 rust/arrow/src/array/transform/mod.rs | 28 ++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/rust/arrow/src/array/transform/mod.rs b/rust/arrow/src/array/transform/mod.rs
index 9c4149ee5f2..074d6acaf11 100644
--- a/rust/arrow/src/array/transform/mod.rs
+++ b/rust/arrow/src/array/transform/mod.rs
@@ -285,10 +285,16 @@ impl<'a> MutableArrayData<'a> {
     /// `use_nulls` is a flag used to optimize insertions. It should be `false` if the only source of nulls
     /// are the arrays themselves and `true` if the user plans to call [MutableArrayData::extend_nulls].
     /// In other words, if `use_nulls` is `false`, calling [MutableArrayData::extend_nulls] should not be used.
-    pub fn new(arrays: Vec<&'a ArrayData>, use_nulls: bool, capacity: usize) -> Self {
+    pub fn new(arrays: Vec<&'a ArrayData>, mut use_nulls: bool, capacity: usize) -> Self {
         let data_type = arrays[0].data_type();
         use crate::datatypes::*;
 
+        // if any of the arrays has nulls, insertions from any array requires setting bits
+        // as there is at least one array with nulls.
+        if arrays.iter().any(|array| array.null_count() > 0) {
+            use_nulls = true;
+        };
+
         let buffers = match &data_type {
             DataType::Boolean => {
                 let bytes = bit_util::ceil(capacity, 8);
@@ -614,6 +620,26 @@ mod tests {
         assert_eq!(result, expected);
     }
 
+    #[test]
+    fn test_multiple_with_nulls() {
+        let array1 = StringArray::from(vec!["hello", "world"]).data();
+        let array2 = StringArray::from(vec![Some("1"), None]).data();
+
+        let arrays = vec![array1.as_ref(), array2.as_ref()];
+
+        let mut mutable = MutableArrayData::new(arrays, false, 5);
+
+        mutable.extend(0, 0, 2);
+        mutable.extend(1, 0, 2);
+
+        let result = mutable.freeze();
+        let result = StringArray::from(Arc::new(result));
+
+        let expected =
+            StringArray::from(vec![Some("hello"), Some("world"), Some("1"), None]);
+        assert_eq!(result, expected);
+    }
+
     #[test]
     fn test_string_null_offset_nulls() {
         let array =