Allocate a buffer of the correct length for ScalarValue::FixedSizeBinary in ScalarValue::to_array_of_size (#18903)

## Which issue does this PR close?

- Closes #18870.

We should open a follow-up issue that tracks re-use
`FixedSizeBinaryArray::new_null` after upgrading arrow-rs.

With this PR, we could backport it to #18843 if we wish.

Alternatively, we could also wait for a fix by arrow-rs.

## Rationale for this change

As we will have to wait for another arrow-rs update to get the fix for
the issue apache/arrow-rs#8901 , we have a
temporaray fix that basically calls the same operations from
DataFusion's code. Once the fix is in the arrow-rs codebase, we can
re-use `FixedSizeBinaryArray::new_null`.

## What changes are included in this PR?

- A test. (`assert_eq!(result.as_fixed_size_binary().values().len(),
10);` returned 0 before)
- Directly allocate the values buffer in DataFusion.

## Are these changes tested?

Yes

## Are there any user-facing changes?

Yes, the buffer will now be allocated, zeroed, and set to the expected
length. Same as in the arrow-rs fix.

Author: tobixdev

datafusion/common/src/scalar/mod.rs

@@ -60,16 +60,16 @@ use arrow::array::{
     BinaryArray, BinaryViewArray, BooleanArray, Date32Array, Date64Array, Decimal32Array,
     Decimal64Array, Decimal128Array, Decimal256Array, DictionaryArray,
     DurationMicrosecondArray, DurationMillisecondArray, DurationNanosecondArray,
-    DurationSecondArray, FixedSizeBinaryArray, FixedSizeListArray, Float16Array,
-    Float32Array, Float64Array, GenericListArray, Int8Array, Int16Array, Int32Array,
-    Int64Array, IntervalDayTimeArray, IntervalMonthDayNanoArray, IntervalYearMonthArray,
-    LargeBinaryArray, LargeListArray, LargeStringArray, ListArray, MapArray,
-    MutableArrayData, OffsetSizeTrait, PrimitiveArray, Scalar, StringArray,
-    StringViewArray, StructArray, Time32MillisecondArray, Time32SecondArray,
-    Time64MicrosecondArray, Time64NanosecondArray, TimestampMicrosecondArray,
-    TimestampMillisecondArray, TimestampNanosecondArray, TimestampSecondArray,
-    UInt8Array, UInt16Array, UInt32Array, UInt64Array, UnionArray, new_empty_array,
-    new_null_array,
+    DurationSecondArray, FixedSizeBinaryArray, FixedSizeBinaryBuilder,
+    FixedSizeListArray, Float16Array, Float32Array, Float64Array, GenericListArray,
+    Int8Array, Int16Array, Int32Array, Int64Array, IntervalDayTimeArray,
+    IntervalMonthDayNanoArray, IntervalYearMonthArray, LargeBinaryArray, LargeListArray,
+    LargeStringArray, ListArray, MapArray, MutableArrayData, OffsetSizeTrait,
+    PrimitiveArray, Scalar, StringArray, StringViewArray, StructArray,
+    Time32MillisecondArray, Time32SecondArray, Time64MicrosecondArray,
+    Time64NanosecondArray, TimestampMicrosecondArray, TimestampMillisecondArray,
+    TimestampNanosecondArray, TimestampSecondArray, UInt8Array, UInt16Array, UInt32Array,
+    UInt64Array, UnionArray, new_empty_array, new_null_array,
 };
 use arrow::buffer::{BooleanBuffer, ScalarBuffer};
 use arrow::compute::kernels::cast::{CastOptions, cast_with_options};
@@ -3059,7 +3059,14 @@ impl ScalarValue {
                     )
                     .unwrap(),
                 ),
-                None => Arc::new(FixedSizeBinaryArray::new_null(*s, size)),
+                None => {
+                    // TODO: Replace with FixedSizeBinaryArray::new_null once a fix for
+                    // https://github.com/apache/arrow-rs/issues/8900 is in the used arrow-rs
+                    // version.
+                    let mut builder = FixedSizeBinaryBuilder::new(*s);
+                    builder.append_nulls(size);
+                    Arc::new(builder.finish())
+                }
             },
             ScalarValue::LargeBinary(e) => match e {
                 Some(value) => Arc::new(
@@ -5317,6 +5324,18 @@ mod tests {
         assert_eq!(empty_array.len(), 0);
     }
 
+    /// See https://github.com/apache/datafusion/issues/18870
+    #[test]
+    fn test_to_array_of_size_for_none_fsb() {
+        let sv = ScalarValue::FixedSizeBinary(5, None);
+        let result = sv
+            .to_array_of_size(2)
+            .expect("Failed to convert to array of size");
+        assert_eq!(result.len(), 2);
+        assert_eq!(result.null_count(), 2);
+        assert_eq!(result.as_fixed_size_binary().values().len(), 10);
+    }
+
     #[test]
     fn test_list_to_array_string() {
         let scalars = vec![