diff --git a/src/Microsoft.ML.AutoML/Experiment/Runners/CrossValSummaryRunner.cs b/src/Microsoft.ML.AutoML/Experiment/Runners/CrossValSummaryRunner.cs
index 0079be3ade..9c382468a6 100644
--- a/src/Microsoft.ML.AutoML/Experiment/Runners/CrossValSummaryRunner.cs
+++ b/src/Microsoft.ML.AutoML/Experiment/Runners/CrossValSummaryRunner.cs
@@ -159,6 +159,19 @@ private static TMetrics GetAverageMetrics(IEnumerable<TMetrics> metrics, TMetric
 
         private static double[] GetAverageOfNonNaNScoresInNestedEnumerable(IEnumerable<IEnumerable<double>> results)
         {
+            if (results.All(result => result == null))
+            {
+                // If all nested enumerables are null, we say the average is a null enumerable as well.
+                // This is expected to happen on Multiclass metrics where the TopKAccuracyForAllK
+                // array can be null if the topKPredictionCount isn't a valid number.
+                // In that case all of the "results" enumerables will be null anyway, and so
+                // returning null is the expected solution.
+                return null;
+            }
+
+            // In case there are only some null elements, we'll ignore them:
+            results = results.Where(result => result != null);
+
             double[] arr = new double[results.ElementAt(0).Count()];
             for (int i = 0; i < arr.Length; i++)
             {
diff --git a/test/Microsoft.ML.AutoML.Tests/AutoFitTests.cs b/test/Microsoft.ML.AutoML.Tests/AutoFitTests.cs
index 14771bb329..86670d5630 100644
--- a/test/Microsoft.ML.AutoML.Tests/AutoFitTests.cs
+++ b/test/Microsoft.ML.AutoML.Tests/AutoFitTests.cs
@@ -42,19 +42,48 @@ public void AutoFitBinaryTest()
             Assert.NotNull(result.BestRun.TrainerName);
         }
 
-        [Fact]
-        public void AutoFitMultiTest()
+        [Theory]
+        [InlineData(true)]
+        [InlineData(false)]
+        public void AutoFitMultiTest(bool useNumberOfCVFolds)
         {
             var context = new MLContext(0);
             var columnInference = context.Auto().InferColumns(DatasetUtil.TrivialMulticlassDatasetPath, DatasetUtil.TrivialMulticlassDatasetLabel);
             var textLoader = context.Data.CreateTextLoader(columnInference.TextLoaderOptions);
             var trainData = textLoader.Load(DatasetUtil.TrivialMulticlassDatasetPath);
-            var result = context.Auto()
-                .CreateMulticlassClassificationExperiment(0)
-                .Execute(trainData, 5, DatasetUtil.TrivialMulticlassDatasetLabel);
-            Assert.True(result.BestRun.Results.First().ValidationMetrics.MicroAccuracy >= 0.7);
-            var scoredData = result.BestRun.Results.First().Model.Transform(trainData);
-            Assert.Equal(NumberDataViewType.Single, scoredData.Schema[DefaultColumnNames.PredictedLabel].Type);
+
+            if (useNumberOfCVFolds)
+            {
+                // When setting numberOfCVFolds
+                // The results object is a CrossValidationExperimentResults<> object
+                uint numberOfCVFolds = 5;
+                var result = context.Auto()
+                    .CreateMulticlassClassificationExperiment(0)
+                    .Execute(trainData, numberOfCVFolds, DatasetUtil.TrivialMulticlassDatasetLabel);
+
+                Assert.True(result.BestRun.Results.First().ValidationMetrics.MicroAccuracy >= 0.7);
+                var scoredData = result.BestRun.Results.First().Model.Transform(trainData);
+                Assert.Equal(NumberDataViewType.Single, scoredData.Schema[DefaultColumnNames.PredictedLabel].Type);
+            }
+            else
+            {
+                // When using this other API, if the trainset is under the
+                // crossValRowCounThreshold, AutoML will also perform CrossValidation
+                // but through a very different path that the one above,
+                // throw a CrossValSummaryRunner and will return
+                // a different type of object as "result" which would now be
+                // simply a ExperimentResult<> object
+
+                int crossValRowCountThreshold = 15000;
+                trainData = context.Data.TakeRows(trainData, crossValRowCountThreshold - 1);
+                var result = context.Auto()
+                    .CreateMulticlassClassificationExperiment(0)
+                    .Execute(trainData, DatasetUtil.TrivialMulticlassDatasetLabel);
+
+                Assert.True(result.BestRun.ValidationMetrics.MicroAccuracy >= 0.7);
+                var scoredData = result.BestRun.Model.Transform(trainData);
+                Assert.Equal(NumberDataViewType.Single, scoredData.Schema[DefaultColumnNames.PredictedLabel].Type);
+            }
         }
 
         [TensorFlowFact]