fix(parquet): guard byte-stream-split encoder release against never-flushed buffer

parquet/internal/encoding/byte_stream_split.go

@@ -94,6 +94,12 @@ var (
 )
 
 func releaseBufferToPool(pooled *PooledBufferWriter) {
+	// the byte-stream-split encoders allocate their flush buffer lazily on the first
+	// FlushValues, so releasing an encoder that never flushed (e.g. a column chunk that
+	// received no values) passes nil here
+	if pooled == nil {
+		return
+	}
 	buf := pooled.buf
 	memory.Set(buf.Buf(), 0)
 	buf.ResizeNoShrink(0)

parquet/internal/encoding/byte_stream_split_release_test.go

@@ -0,0 +1,52 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package encoding
+
+import (
+	"testing"
+
+	"github.com/apache/arrow-go/v18/arrow/memory"
+	"github.com/apache/arrow-go/v18/parquet"
+	"github.com/apache/arrow-go/v18/parquet/schema"
+	"github.com/stretchr/testify/assert"
+)
+
+// The byte-stream-split encoders allocate their flush buffer lazily on the first
+// FlushValues, so an encoder released without ever flushing (as columnWriter.Close
+// does for a column chunk that received no values) must not dereference the nil buffer.
+func TestByteStreamSplitReleaseWithoutFlush(t *testing.T) {
+	tests := []struct {
+		name    string
+		typ     parquet.Type
+		typeLen int32
+	}{
+		{"int32", parquet.Types.Int32, -1},
+		{"int64", parquet.Types.Int64, -1},
+		{"float32", parquet.Types.Float, -1},
+		{"float64", parquet.Types.Double, -1},
+		{"fixed_len_byte_array", parquet.Types.FixedLenByteArray, 4},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			descr := schema.NewColumn(schema.MustPrimitive(schema.NewPrimitiveNode(
+				"col", parquet.Repetitions.Required, tt.typ, -1, tt.typeLen)), 0, 0)
+			enc := NewEncoder(tt.typ, parquet.Encodings.ByteStreamSplit, false, descr, memory.DefaultAllocator)
+			assert.NotPanics(t, enc.Release)
+		})
+	}
+}