[ES|QL] Fix NPE in the completion operator.

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/inference/bulk/BulkInferenceExecutionState.java

@@ -75,7 +75,7 @@ public void markSeqNoAsPersisted(long seqNo) {
      *  @param response The inference response.
      */
     public synchronized void onInferenceResponse(long seqNo, InferenceAction.Response response) {
-        if (failureCollector.hasFailure() == false) {
+        if (response != null && failureCollector.hasFailure() == false) {
             bufferedResponses.put(seqNo, response);
         }
         checkpoint.markSeqNoAsProcessed(seqNo);

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/inference/bulk/BulkInferenceExecutor.java

@@ -69,16 +69,19 @@ public void execute(BulkInferenceRequestIterator requests, ActionListener<List<I
                 bulkExecutionState.finish();
             }
 
-            throttledInferenceRunner.doInference(
-                request,
-                ActionListener.runAfter(
-                    ActionListener.wrap(
-                        r -> bulkExecutionState.onInferenceResponse(seqNo, r),
-                        e -> bulkExecutionState.onInferenceException(seqNo, e)
-                    ),
-                    responseHandler::persistPendingResponses
-                )
+            ActionListener<InferenceAction.Response> inferenceResponseListener = ActionListener.runAfter(
+                ActionListener.wrap(
+                    r -> bulkExecutionState.onInferenceResponse(seqNo, r),
+                    e -> bulkExecutionState.onInferenceException(seqNo, e)
+                ),
+                responseHandler::persistPendingResponses
             );
+
+            if (request == null) {
+                inferenceResponseListener.onResponse(null);
+            } else {
+                throttledInferenceRunner.doInference(request, inferenceResponseListener);
+            }
         }
     }
 
@@ -112,7 +115,6 @@ public synchronized void persistPendingResponses() {
                 if (bulkExecutionState.hasFailure() == false) {
                     try {
                         InferenceAction.Response response = bulkExecutionState.fetchBufferedResponse(persistedSeqNo);
-                        assert response != null;
                         responses.add(response);
                     } catch (Exception e) {
                         bulkExecutionState.addFailure(e);

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/inference/completion/CompletionOperatorOutputBuilder.java

@@ -51,6 +51,11 @@ public void close() {
      */
     @Override
     public void addInferenceResponse(InferenceAction.Response inferenceResponse) {
+        if (inferenceResponse == null) {
+            outputBlockBuilder.appendNull();
+            return;
+        }
+
         ChatCompletionResults completionResults = inferenceResults(inferenceResponse);
 
         if (completionResults == null) {

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/inference/completion/CompletionOperatorRequestIterator.java

@@ -58,6 +58,10 @@ public InferenceAction.Request next() {
      * Wraps a single prompt string into an {@link InferenceAction.Request}.
      */
     private InferenceAction.Request inferenceRequest(String prompt) {
+        if (prompt == null) {
+            return null;
+        }
+
         return InferenceAction.Request.builder(inferenceId, TaskType.COMPLETION).setInput(List.of(prompt)).build();
     }
 

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/inference/InferenceOperatorTestCase.java

@@ -88,12 +88,17 @@ protected int remaining() {
             @Override
             protected Page createPage(int positionOffset, int length) {
                 length = Integer.min(length, remaining());
-                try (var builder = blockFactory.newBytesRefVectorBuilder(length)) {
+                try (var builder = blockFactory.newBytesRefBlockBuilder(length)) {
                     for (int i = 0; i < length; i++) {
-                        builder.appendBytesRef(new BytesRef(randomAlphaOfLength(10)));
+                        if (randomInt() % 100 == 0) {
+                            builder.appendNull();
+                        } else {
+                            builder.appendBytesRef(new BytesRef(randomAlphaOfLength(10)));
+                        }
+
                     }
                     currentPosition += length;
-                    return new Page(builder.build().asBlock());
+                    return new Page(builder.build());
                 }
             }
         };