The change for map support.

sql/core/src/main/java/org/apache/spark/sql/execution/vectorized/WritableColumnVector.java

@@ -624,6 +624,7 @@ public final ColumnarArray getArray(int rowId) {
   // second child column vector, and puts the offsets and lengths in the current column vector.
   @Override
   public final ColumnarMap getMap(int rowId) {
+    if (isNullAt(rowId)) return null;
     return new ColumnarMap(getChild(0), getChild(1), getArrayOffset(rowId), getArrayLength(rowId));
   }
 

sql/core/src/main/java/org/apache/spark/sql/vectorized/ColumnVector.java

@@ -233,13 +233,13 @@ public final ColumnarRow getStruct(int rowId) {
   public abstract ColumnarArray getArray(int rowId);
 
   /**
-   * Returns the map type value for rowId.
+   * Returns the map type value for rowId. If the slot for rowId is null, it should return null.
    *
    * In Spark, map type value is basically a key data array and a value data array. A key from the
    * key array with a index and a value from the value array with the same index contribute to
    * an entry of this map type value.
    *
-   * To support map type, implementations must construct an {@link ColumnarMap} and return it in
+   * To support map type, implementations must construct a {@link ColumnarMap} and return it in
    * this method. {@link ColumnarMap} requires a {@link ColumnVector} that stores the data of all
    * the keys of all the maps in this vector, and another {@link ColumnVector} that stores the data
    * of all the values of all the maps in this vector, and a pair of offset and length which

sql/core/src/main/java/org/apache/spark/sql/vectorized/ColumnarRow.java

@@ -150,7 +150,6 @@ public ColumnarArray getArray(int ordinal) {
 
   @Override
   public ColumnarMap getMap(int ordinal) {
-    if (data.getChild(ordinal).isNullAt(rowId)) return null;
     return data.getChild(ordinal).getMap(rowId);
   }
 

sql/core/src/test/scala/org/apache/spark/sql/execution/vectorized/ColumnarBatchSuite.scala

@@ -1373,4 +1373,28 @@ class ColumnarBatchSuite extends SparkFunSuite {
       column.putByteArray(idx, "Hello".getBytes(StandardCharsets.UTF_8))
       assert(column.getBinary(idx) != null)
   }
+
+  testVector("getMap should return null for null slot", 4,
+    new MapType(IntegerType, IntegerType, false)) { column =>
+      assert(column.numNulls() == 0)
+
+      var idx = 0
+      column.putNull(idx)
+      assert(column.getBinary(idx) == null)
+      idx += 1
+      column.putNull(idx)
+      assert(column.getBinary(idx) == null)
+      assert(column.numNulls() == 2)
+
+      idx += 1
+      val keyCol = column.getChild(0)
+      keyCol.putInt(0, 0)
+      keyCol.putInt(1, 1)
+      val valueCol = column.getChild(1)
+      valueCol.putInt(0, 0)
+      valueCol.putInt(1, 2)
+
+      column.putArray(idx, 0, 2)
+      assert(column.getMap(idx) != null)
+  }
 }