Code review,

Author: DmitryLukyanov

src/MongoDB.Driver.Core/Core/Encryption/EncryptedCollectionHelper.cs

@@ -85,24 +85,14 @@ public static IEnumerable<BsonDocument> IterateEmptyKeyIds(CollectionNamespace c
 
             if (storedEncryptedFields.TryGetValue("fields", out var fields) && fields is BsonArray fieldsArray)
             {
-                foreach (var field in fieldsArray)
+                foreach (var field in fieldsArray.OfType<BsonDocument>()) // If `F` is not a document element, skip it.
                 {
-                    if (field is BsonDocument fieldDocument)
+                    if (field.TryGetElement("keyId", out var keyId) && keyId.Value == BsonNull.Value)
                     {
-                        if (fieldDocument.TryGetElement("keyId", out var keyId) && keyId.Value == BsonNull.Value)
-                        {
-                            yield return fieldDocument;
-                        }
-                    }
-                    else
-                    {
-                        // If `F` is not a document element, skip it.
-                        continue;
+                        yield return field;
                     }
                 }
             }
-
-            yield break;
         }
 
         public static void ModifyEndryptedFields(BsonDocument fieldDocument, Guid dataKey)

tests/MongoDB.Driver.Tests/Specifications/client-side-encryption/prose-tests/ClientEncryptionProseTests.cs

@@ -133,11 +133,9 @@ void RunTestCase(int testCase)
                         case 3: // Case 3: Invalid ``keyId``
                             {
                                 var effectiveEncryptedFields = encryptedFields.DeepClone();
-                                effectiveEncryptedFields["fields"].AsBsonArray[0].AsBsonDocument["keyId"] = true;
-                                var collection = CreateEncryptedCollection(client, clientEncryption, __collCollectionNamespace, encryptedFields, kmsProvider, async).Collection;
-
-                                var exception = Record.Exception(() => Insert(collection, async, new BsonDocument("ssn", "123-45-6789")));
-                                exception.Should().BeOfType<MongoBulkWriteException<BsonDocument>>().Which.Message.Should().Contain("Document failed validation");
+                                effectiveEncryptedFields["fields"].AsBsonArray[0].AsBsonDocument["keyId"] = false;
+                                var exception = Record.Exception(() => CreateEncryptedCollection(client, clientEncryption, __collCollectionNamespace, effectiveEncryptedFields.AsBsonDocument, kmsProvider, async));
+                                exception.Should().BeOfType<MongoCommandException>().Which.Message.Should().Contain("BSON field 'create.encryptedFields.fields.keyId' is the wrong type 'bool', expected type 'binData'");
                             }
                             break;
                         default: throw new Exception($"Unexpected test case {testCase}.");