Add test

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

@@ -554,7 +554,7 @@ final int getArrayOffset(int rowId) {
   }
 
   /**
-   * This is a place holder class. Any "get" method will throw UnsupportedOperationException.
+   * Any call to "get" method will throw UnsupportedOperationException.
    *
    * Access struct values in a ArrowColumnVector doesn't use this accessor. Instead, it uses getStruct() method defined
    * in the parent class. Any call to "get" method in this class is a bug in the code.

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

@@ -322,6 +322,42 @@ class ArrowColumnVectorSuite extends SparkFunSuite {
     allocator.close()
   }
 
+  test("non nullable struct") {
+    val allocator = ArrowUtils.rootAllocator.newChildAllocator("struct", 0, Long.MaxValue)
+    val schema = new StructType().add("int", IntegerType).add("long", LongType)
+    val vector = ArrowUtils.toArrowField("struct", schema, nullable = false, null)
+      .createVector(allocator).asInstanceOf[NullableMapVector]
+
+    vector.allocateNew()
+    val intVector = vector.getChildByOrdinal(0).asInstanceOf[IntVector]
+    val longVector = vector.getChildByOrdinal(1).asInstanceOf[BigIntVector]
+
+    vector.setIndexDefined(0)
+    intVector.setSafe(0, 1)
+    longVector.setSafe(0, 1L)
+
+    vector.setIndexDefined(1)
+    intVector.setSafe(1, 2)
+    longVector.setNull(1)
+
+    vector.setValueCount(2)
+
+    val columnVector = new ArrowColumnVector(vector)
+    assert(columnVector.dataType === schema)
+    assert(columnVector.numNulls === 0)
+
+    val row0 = columnVector.getStruct(0, 2)
+    assert(row0.getInt(0) === 1)
+    assert(row0.getLong(1) === 1L)
+
+    val row1 = columnVector.getStruct(1, 2)
+    assert(row1.getInt(0) === 2)
+    assert(row1.isNullAt(1))
+
+    columnVector.close()
+    allocator.close()
+  }
+
   test("struct") {
     val allocator = ArrowUtils.rootAllocator.newChildAllocator("struct", 0, Long.MaxValue)
     val schema = new StructType().add("int", IntegerType).add("long", LongType)