[FormRecognizer] Fix: client can now parse results with null fields

sdk/formrecognizer/Azure.AI.FormRecognizer/CHANGELOG.md

@@ -25,6 +25,7 @@
 - Custom form recognition without labels can now handle multipaged forms.
 - `RecognizedForm.Pages` now only contains pages whose numbers are within `RecognizedForm.PageRange`.
 - `FieldText.TextContent` cannot be `null` anymore, and it will be empty when no element is returned from the service.
+- Custom form recognition with labels can now parse results from forms that do not contain all of the expected labels ([#11821](https://github.com/Azure/azure-sdk-for-net/issues/11821)).
 
 ## 1.0.0-preview.2 (05-06-2020)
 

sdk/formrecognizer/Azure.AI.FormRecognizer/src/FormTrainingClient.cs

@@ -34,7 +34,7 @@ protected FormTrainingClient()
         /// <summary>
         /// Initializes a new instance of the <see cref="FormTrainingClient"/> class.
         /// </summary>
-        /// <param name="endpoint">The endpoint to use for connecting to the Form Recognizer Azure Cognitive Service. The URI is likely to be similar to <c>{protocol}://{resourcename}.cognitiveservices.azure.com</c>.</param>
+        /// <param name="endpoint">The endpoint to use for connecting to the Form Recognizer Azure Cognitive Service.</param>
         /// <param name="credential">A credential used to authenticate to an Azure Service.</param>
         /// <remarks>
         /// Both the <paramref name="endpoint"/> URI <c>string</c> and the <paramref name="credential"/> <c>string</c> key
@@ -48,7 +48,7 @@ protected FormTrainingClient()
         /// <summary>
         /// Initializes a new instance of the <see cref="FormTrainingClient"/> class.
         /// </summary>
-        /// <param name="endpoint">The endpoint to use for connecting to the Form Recognizer Azure Cognitive Service. The URI is likely to be similar to <c>{protocol}://{resourcename}.cognitiveservices.azure.com</c>.</param>
+        /// <param name="endpoint">The endpoint to use for connecting to the Form Recognizer Azure Cognitive Service.</param>
         /// <param name="credential">A credential used to authenticate to an Azure Service.</param>
         /// <param name="options">A set of options to apply when configuring the client.</param>
         /// <remarks>

sdk/formrecognizer/Azure.AI.FormRecognizer/src/RecognizedForm.cs

@@ -81,7 +81,9 @@ private static IReadOnlyDictionary<string, FormField> ConvertSupervisedFields(IR
 
             foreach (var field in fields)
             {
-                fieldDictionary[field.Key] = new FormField(field.Key, field.Value, readResults);
+                fieldDictionary[field.Key] = field.Value == null
+                    ? null
+                    : new FormField(field.Key, field.Value, readResults);
             }
 
             return fieldDictionary;

sdk/formrecognizer/Azure.AI.FormRecognizer/tests/FormRecognizerClient/FormRecognizerClientLiveTests.cs

@@ -474,6 +474,43 @@ public async Task StartRecognizeCustomFormsWithLabelsCanParseMultipageForms(bool
             }
         }
 
+        [Test]
+        [TestCase(true)]
+        [TestCase(false)]
+        public async Task StartRecognizeCustomFormsWithLabelsCanParseDifferentTypeOfForm(bool useStream)
+        {
+            var client = CreateInstrumentedFormRecognizerClient();
+            RecognizeCustomFormsOperation operation;
+
+            // Use Form_<id>.<ext> files for training with labels.
+
+            await using var trainedModel = await CreateDisposableTrainedModelAsync(useTrainingLabels: true);
+
+            // Attempt to recognize a different type of form: Invoice_1.pdf. This form does not contain all the labels
+            // the newly trained model expects.
+
+            if (useStream)
+            {
+                using var stream = new FileStream(FormRecognizerTestEnvironment.RetrieveInvoicePath(1, ContentType.Pdf), FileMode.Open);
+                using (Recording.DisableRequestBodyRecording())
+                {
+                    operation = await client.StartRecognizeCustomFormsAsync(trainedModel.ModelId, stream);
+                }
+            }
+            else
+            {
+                var uri = new Uri(FormRecognizerTestEnvironment.RetrieveInvoiceUri(1));
+                operation = await client.StartRecognizeCustomFormsFromUriAsync(trainedModel.ModelId, uri);
+            }
+
+            RecognizedFormCollection forms = await operation.WaitForCompletionAsync();
+            var fields = forms.Single().Fields;
+
+            // Verify that we got back at least one null field to make sure we hit the code path we want to test.
+
+            Assert.IsTrue(fields.Any(kvp => kvp.Value == null));
+        }
+
         /// <summary>
         /// Verifies that the <see cref="FormRecognizerClient" /> is able to connect to the Form
         /// Recognizer cognitive service and perform analysis based on a custom labeled model.