JavaScriptAggregatorFactory: Handle missing columns by passing down null args

processing/src/main/java/io/druid/query/aggregation/JavaScriptAggregatorFactory.java

@@ -265,9 +265,11 @@ public class JavaScriptAggregatorFactory implements AggregatorFactory
         final Object[] args = new Object[size + 1];
 
         args[0] = current;
-        int i = 0;
-        while (i < size) {
-          args[i + 1] = selectorList[i++].get();
+        for (int i = 0 ; i < size ; i++) {
+          final ObjectColumnSelector selector = selectorList[i];
+          if (selector != null) {
+            args[i + 1] = selector.get();
+          }
         }
 
         final Object res = fnAggregate.call(cx, scope, scope, args);

processing/src/test/java/io/druid/query/aggregation/JavaScriptAggregatorTest.java

@@ -27,6 +27,7 @@ import org.junit.Test;
 
 import java.nio.ByteBuffer;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.Map;
 
 public class JavaScriptAggregatorTest
@@ -141,6 +142,39 @@ public class JavaScriptAggregatorTest
     Assert.assertEquals(val, agg.get(buf, position));
   }
 
+  @Test
+  public void testAggregateMissingColumn()
+  {
+    Map<String, String> script = scriptDoubleSum;
+
+    JavaScriptAggregator agg = new JavaScriptAggregator(
+        "billy",
+        Collections.<ObjectColumnSelector>singletonList(null),
+        JavaScriptAggregatorFactory.compileScript(script.get("fnAggregate"),
+                                                  script.get("fnReset"),
+                                                  script.get("fnCombine"))
+    );
+
+    final double val = 0;
+
+    Assert.assertEquals("billy", agg.getName());
+
+    agg.reset();
+    Assert.assertEquals(val, agg.get());
+    Assert.assertEquals(val, agg.get());
+    Assert.assertEquals(val, agg.get());
+
+    agg.aggregate();
+    Assert.assertEquals(val, agg.get());
+    Assert.assertEquals(val, agg.get());
+    Assert.assertEquals(val, agg.get());
+
+    agg.aggregate();
+    Assert.assertEquals(val, agg.get());
+    Assert.assertEquals(val, agg.get());
+    Assert.assertEquals(val, agg.get());
+  }
+
   public static void main(String... args) throws Exception {
     final LoopingFloatColumnSelector selector = new LoopingFloatColumnSelector(new float[]{42.12f, 9f});