fix: change constructor instead

Author: Yicong-Huang

sql/catalyst/src/main/scala/org/apache/spark/sql/execution/arrow/ArrowWriter.scala

@@ -387,6 +387,11 @@ private[arrow] class ArrayWriter(
     val valueVector: ListVector,
     val elementWriter: ArrowFieldWriter) extends ArrowFieldWriter {
 
+  // SPARK-55056: Arrow format requires ListArray offset buffer to have N+1 entries.
+  // Even when N=0, the buffer must contain [0]. Initialize offset buffer at construction
+  // to ensure it exists even if no elements are written.
+  valueVector.getOffsetBuffer.setInt(0, 0)
+
   override def setNull(): Unit = {
   }
 
@@ -402,17 +407,6 @@ private[arrow] class ArrayWriter(
   }
 
   override def finish(): Unit = {
-    // SPARK-55056: Arrow format requires ListArray offset buffer to have N+1 entries.
-    // Even when N=0, the buffer must contain [0]. When the outer array is empty,
-    // nested ArrayWriters are never invoked, so their count stays 0. Then
-    // getBufferSizeFor(0) returns 0, and the offset buffer is omitted in IPC
-    // serialization — violating Arrow spec. Simulate one empty write to ensure
-    // the offset buffer is properly initialized.
-    if (count == 0) {
-      valueVector.startNewValue(0)
-      valueVector.endValue(0, 0)
-      count = 1
-    }
     super.finish()
     elementWriter.finish()
   }