Fix the bug in string last vector aggregation (#14655)

processing/src/main/java/org/apache/druid/query/aggregation/last/StringLastVectorAggregator.java

@@ -42,7 +42,7 @@ public class StringLastVectorAggregator implements VectorAggregator
   protected long lastTime;
 
   public StringLastVectorAggregator(
-      final BaseLongVectorValueSelector timeSelector,
+      @Nullable final BaseLongVectorValueSelector timeSelector,
       final VectorObjectSelector valueSelector,
       final int maxStringBytes
   )
@@ -124,6 +124,9 @@ public class StringLastVectorAggregator implements VectorAggregator
       int positionOffset
   )
   {
+    if (timeSelector == null) {
+      return;
+    }
     long[] timeVector = timeSelector.getLongVector();
     Object[] objectsWhichMightBeStrings = valueSelector.getObjectVector();
 

processing/src/test/java/org/apache/druid/query/aggregation/last/StringLastVectorAggregatorTest.java

@@ -129,6 +129,25 @@ public class StringLastVectorAggregatorTest extends InitializedNullHandlingTest
     Assert.assertEquals(VALUES[3], result.rhs);
   }
 
+  @Test
+  public void aggregateNoOp()
+  {
+    // Test that aggregates run just fine when the input field does not exist
+    StringLastVectorAggregator aggregator = new StringLastVectorAggregator(null, selector, 10);
+    aggregator.aggregate(buf, 0, 0, VALUES.length);
+  }
+
+  @Test
+  public void aggregateBatchNoOp()
+  {
+    // Test that aggregates run just fine when the input field does not exist
+    StringLastVectorAggregator aggregator = new StringLastVectorAggregator(null, selector, 10);
+    int[] positions = new int[]{0, 43, 70};
+    int positionOffset = 2;
+    clearBufferForPositions(positionOffset, positions);
+    aggregator.aggregate(buf, 3, positions, null, positionOffset);
+  }
+
   @Test
   public void aggregateBatchWithoutRows()
   {