Declare Annotations as nullable to prevent null reference assignment

Author: MaggieKimani1

src/Microsoft.OpenApi/Models/OpenApiDocument.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft Corporation. All rights reserved.
+// Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT license.
 
 using System;
@@ -89,7 +89,7 @@ public class OpenApiDocument : IOpenApiSerializable, IOpenApiExtensible, IOpenAp
         public string HashCode => GenerateHashValue(this);
 
         /// <inheritdoc />
-        public IDictionary<string, object> Annotations { get; set; }
+        public IDictionary<string, object>? Annotations { get; set; }
 
         /// <summary>
         /// Implements IBaseDocument

src/Microsoft.OpenApi/Models/OpenApiOperation.cs

@@ -109,7 +109,7 @@ public class OpenApiOperation : IOpenApiSerializable, IOpenApiExtensible, IOpenA
         public IDictionary<string, IOpenApiExtension>? Extensions { get; set; } = new Dictionary<string, IOpenApiExtension>();
 
         /// <inheritdoc />
-        public IDictionary<string, object> Annotations { get; set; }
+        public IDictionary<string, object>? Annotations { get; set; }
 
         /// <summary>
         /// Parameterless constructor

test/Microsoft.OpenApi.Hidi.Tests/Services/OpenApiFilterServiceTests.cs

@@ -237,17 +237,19 @@ public void CopiesOverAllReferencedComponentsToTheSubsetDocumentCorrectly()
             var predicate = OpenApiFilterService.CreatePredicate(operationIds: operationIds);
             var subsetOpenApiDocument = OpenApiFilterService.CreateFilteredDocument(doc, predicate);
 
-            var response = subsetOpenApiDocument.Paths["/items"].Operations[OperationType.Get].Responses["200"];
-            var responseHeader = response.Headers["x-custom-header"];
-            var mediaTypeExample = response.Content["application/json"].Examples.First().Value;
-            var targetHeaders = subsetOpenApiDocument.Components.Headers;
-            var targetExamples = subsetOpenApiDocument.Components.Examples;
+            var response = subsetOpenApiDocument.Paths["/items"].Operations[OperationType.Get]?.Responses?["200"];
+            var responseHeader = response?.Headers["x-custom-header"];
+            var mediaTypeExample = response?.Content["application/json"]?.Examples?.First().Value;
+            var targetHeaders = subsetOpenApiDocument.Components?.Headers;
+            var targetExamples = subsetOpenApiDocument.Components?.Examples;
 
             // Assert
             Assert.Same(doc.Servers, subsetOpenApiDocument.Servers);
-            Assert.False(responseHeader.UnresolvedReference);
-            Assert.False(mediaTypeExample.UnresolvedReference);
+            Assert.False(responseHeader?.UnresolvedReference);
+            Assert.False(mediaTypeExample?.UnresolvedReference);
+            Assert.NotNull(targetHeaders);
             Assert.Single(targetHeaders);
+            Assert.NotNull(targetExamples);
             Assert.Single(targetExamples);
         }
 

test/Microsoft.OpenApi.Tests/PublicApi/PublicApi.approved.txt

@@ -543,7 +543,7 @@ namespace Microsoft.OpenApi.Models
     {
         public OpenApiDocument() { }
         public OpenApiDocument(Microsoft.OpenApi.Models.OpenApiDocument? document) { }
-        public System.Collections.Generic.IDictionary<string, object> Annotations { get; set; }
+        public System.Collections.Generic.IDictionary<string, object>? Annotations { get; set; }
         public System.Uri BaseUri { get; }
         public Microsoft.OpenApi.Models.OpenApiComponents? Components { get; set; }
         public System.Collections.Generic.IDictionary<string, Microsoft.OpenApi.Interfaces.IOpenApiExtension>? Extensions { get; set; }
@@ -741,7 +741,7 @@ namespace Microsoft.OpenApi.Models
         public const bool DeprecatedDefault = false;
         public OpenApiOperation() { }
         public OpenApiOperation(Microsoft.OpenApi.Models.OpenApiOperation? operation) { }
-        public System.Collections.Generic.IDictionary<string, object> Annotations { get; set; }
+        public System.Collections.Generic.IDictionary<string, object>? Annotations { get; set; }
         public System.Collections.Generic.IDictionary<string, Microsoft.OpenApi.Models.OpenApiCallback>? Callbacks { get; set; }
         public bool Deprecated { get; set; }
         public string? Description { get; set; }
@@ -1529,7 +1529,7 @@ namespace Microsoft.OpenApi.Services
         public System.Uri GetDocumentId(string key) { }
         public bool RegisterComponent<T>(string location, T component) { }
         public void RegisterComponents(Microsoft.OpenApi.Models.OpenApiDocument document) { }
-        public T ResolveReference<T>(string location) { }
+        public T? ResolveReference<T>(string location) { }
     }
     public class OperationSearch : Microsoft.OpenApi.Services.OpenApiVisitorBase
     {