Enables null reference types

src/Microsoft.OpenApi/Interfaces/IOpenApiExtensible.cs

@@ -13,6 +13,6 @@ public interface IOpenApiExtensible : IOpenApiElement
         /// <summary>
         /// Specification extensions.
         /// </summary>
-        IDictionary<string, IOpenApiExtension> Extensions { get; set; }
+        IDictionary<string, IOpenApiExtension>? Extensions { get; set; }
     }
 }

src/Microsoft.OpenApi/Interfaces/IOpenApiReader.cs

@@ -21,7 +21,7 @@ public interface IOpenApiReader
         /// <param name="settings"> The OpenApi reader settings.</param>
         /// <param name="cancellationToken">Propagates notification that an operation should be cancelled.</param>
         /// <returns></returns>
-        Task<ReadResult> ReadAsync(TextReader input, OpenApiReaderSettings settings = null, CancellationToken cancellationToken = default);
+        Task<ReadResult> ReadAsync(TextReader input, OpenApiReaderSettings? settings = null, CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Parses the JsonNode input into an Open API document.
@@ -31,7 +31,7 @@ public interface IOpenApiReader
         /// <param name="cancellationToken">Propagates notifications that operations should be cancelled.</param>
         /// <param name="format">The OpenAPI format.</param>
         /// <returns></returns>
-        Task<ReadResult> ReadAsync(JsonNode jsonNode, OpenApiReaderSettings settings, string format = null, CancellationToken cancellationToken = default);
+        Task<ReadResult> ReadAsync(JsonNode jsonNode, OpenApiReaderSettings settings, string? format = null, CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Reads the TextReader input and parses the fragment of an OpenAPI description into an Open API Element.
@@ -41,7 +41,7 @@ public interface IOpenApiReader
         /// <param name="diagnostic">Returns diagnostic object containing errors detected during parsing.</param>
         /// <param name="settings">The OpenApiReader settings.</param>
         /// <returns>Instance of newly created IOpenApiElement.</returns>
-        T ReadFragment<T>(TextReader input, OpenApiSpecVersion version, out OpenApiDiagnostic diagnostic, OpenApiReaderSettings settings = null) where T : IOpenApiElement;
+        T ReadFragment<T>(TextReader input, OpenApiSpecVersion version, out OpenApiDiagnostic diagnostic, OpenApiReaderSettings? settings = null) where T : IOpenApiElement;
 
         /// <summary>
         /// Reads the JsonNode input and parses the fragment of an OpenAPI description into an Open API Element.
@@ -51,6 +51,6 @@ public interface IOpenApiReader
         /// <param name="diagnostic">Returns diagnostic object containing errors detected during parsing.</param>
         /// <param name="settings">The OpenApiReader settings.</param>
         /// <returns>Instance of newly created IOpenApiElement.</returns>
-        T ReadFragment<T>(JsonNode input, OpenApiSpecVersion version, out OpenApiDiagnostic diagnostic, OpenApiReaderSettings settings = null) where T : IOpenApiElement;
+        T ReadFragment<T>(JsonNode input, OpenApiSpecVersion version, out OpenApiDiagnostic diagnostic, OpenApiReaderSettings? settings = null) where T : IOpenApiElement;
     }
 }

src/Microsoft.OpenApi/Interfaces/IOpenApiReferenceable.cs

@@ -19,7 +19,7 @@ public interface IOpenApiReferenceable : IOpenApiSerializable
         /// <summary>
         /// Reference object.
         /// </summary>
-        OpenApiReference Reference { get; set; }
+        OpenApiReference? Reference { get; set; }
 
         /// <summary>
         /// Serialize to OpenAPI V31 document without using reference.

src/Microsoft.OpenApi/Microsoft.OpenApi.csproj

@@ -2,6 +2,7 @@
     <PropertyGroup>
         <TargetFramework>netstandard2.0</TargetFramework>
         <LangVersion>Latest</LangVersion>
+        <Nullable>enable</Nullable>
         <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
         <Version>1.6.11</Version>
         <Description>.NET models with JSON and YAML writers for OpenAPI specification</Description>

src/Microsoft.OpenApi/Models/OpenApiCallback.cs

@@ -17,7 +17,7 @@ public class OpenApiCallback : IOpenApiReferenceable, IOpenApiExtensible, IEffec
         /// <summary>
         /// A Path Item Object used to define a callback request and expected responses.
         /// </summary>
-        public virtual Dictionary<RuntimeExpression, OpenApiPathItem> PathItems { get; set; }
+        public virtual Dictionary<RuntimeExpression, OpenApiPathItem>? PathItems { get; set; }
             = new();
 
         /// <summary>
@@ -28,12 +28,12 @@ public class OpenApiCallback : IOpenApiReferenceable, IOpenApiExtensible, IEffec
         /// <summary>
         /// Reference pointer.
         /// </summary>
-        public OpenApiReference Reference { get; set; }
+        public OpenApiReference? Reference { get; set; }
 
         /// <summary>
         /// This object MAY be extended with Specification Extensions.
         /// </summary>
-        public virtual IDictionary<string, IOpenApiExtension> Extensions { get; set; } = new Dictionary<string, IOpenApiExtension>();
+        public virtual IDictionary<string, IOpenApiExtension>? Extensions { get; set; } = new Dictionary<string, IOpenApiExtension>();
 
         /// <summary>
         /// Parameter-less constructor
@@ -45,9 +45,9 @@ public OpenApiCallback() { }
         /// </summary>
         public OpenApiCallback(OpenApiCallback callback)
         {
-            PathItems = callback?.PathItems != null ? new(callback?.PathItems) : null;
+            PathItems = callback?.PathItems != null ? new(callback.PathItems) : null;
             UnresolvedReference = callback?.UnresolvedReference ?? UnresolvedReference;
-            Reference = callback?.Reference != null ? new(callback?.Reference) : null;
+            Reference = callback?.Reference != null ? new(callback.Reference) : null;
             Extensions = callback?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(callback.Extensions) : null;
         }
 
@@ -160,13 +160,16 @@ internal void SerializeInternalWithoutReference(IOpenApiWriter writer, OpenApiSp
             writer.WriteStartObject();
 
             // path items
-            foreach (var item in PathItems)
+            if (PathItems != null)
             {
-                writer.WriteRequiredObject(item.Key.Expression, item.Value, callback);
-            }
+                foreach (var item in PathItems)
+                {
+                    writer.WriteRequiredObject(item.Key.Expression, item.Value, callback);
+                }
+            }            
 
             // extensions
-            writer.WriteExtensions(Extensions, version);
+            writer.WriteExtensions(Extensions!, version);
 
             writer.WriteEndObject();
         }

src/Microsoft.OpenApi/Models/OpenApiComponents.cs

@@ -19,60 +19,60 @@ public class OpenApiComponents : IOpenApiSerializable, IOpenApiExtensible
         /// <summary>
         /// An object to hold reusable <see cref="JsonSchema"/> Objects.
         /// </summary>
-        public IDictionary<string, JsonSchema> Schemas { get; set; } = new Dictionary<string, JsonSchema>();
+        public IDictionary<string, JsonSchema>? Schemas { get; set; } = new Dictionary<string, JsonSchema>();
 
         /// <summary>
         /// An object to hold reusable <see cref="OpenApiResponse"/> Objects.
         /// </summary>
-        public virtual IDictionary<string, OpenApiResponse> Responses { get; set; } = new Dictionary<string, OpenApiResponse>();
+        public virtual IDictionary<string, OpenApiResponse>? Responses { get; set; } = new Dictionary<string, OpenApiResponse>();
 
         /// <summary>
         /// An object to hold reusable <see cref="OpenApiParameter"/> Objects.
         /// </summary>
-        public virtual IDictionary<string, OpenApiParameter> Parameters { get; set; } =
+        public virtual IDictionary<string, OpenApiParameter>? Parameters { get; set; } =
             new Dictionary<string, OpenApiParameter>();
 
         /// <summary>
         /// An object to hold reusable <see cref="OpenApiExample"/> Objects.
         /// </summary>
-        public virtual IDictionary<string, OpenApiExample> Examples { get; set; } = new Dictionary<string, OpenApiExample>();
+        public virtual IDictionary<string, OpenApiExample>? Examples { get; set; } = new Dictionary<string, OpenApiExample>();
 
         /// <summary>
         /// An object to hold reusable <see cref="OpenApiRequestBody"/> Objects.
         /// </summary>
-        public virtual IDictionary<string, OpenApiRequestBody> RequestBodies { get; set; } =
+        public virtual IDictionary<string, OpenApiRequestBody>? RequestBodies { get; set; } =
             new Dictionary<string, OpenApiRequestBody>();
 
         /// <summary>
         /// An object to hold reusable <see cref="OpenApiHeader"/> Objects.
         /// </summary>
-        public virtual IDictionary<string, OpenApiHeader> Headers { get; set; } = new Dictionary<string, OpenApiHeader>();
+        public virtual IDictionary<string, OpenApiHeader>? Headers { get; set; } = new Dictionary<string, OpenApiHeader>();
 
         /// <summary>
         /// An object to hold reusable <see cref="OpenApiSecurityScheme"/> Objects.
         /// </summary>
-        public virtual IDictionary<string, OpenApiSecurityScheme> SecuritySchemes { get; set; } =
+        public virtual IDictionary<string, OpenApiSecurityScheme>? SecuritySchemes { get; set; } =
             new Dictionary<string, OpenApiSecurityScheme>();
 
         /// <summary>
         /// An object to hold reusable <see cref="OpenApiLink"/> Objects.
         /// </summary>
-        public virtual IDictionary<string, OpenApiLink> Links { get; set; } = new Dictionary<string, OpenApiLink>();
+        public virtual IDictionary<string, OpenApiLink>? Links { get; set; } = new Dictionary<string, OpenApiLink>();
 
         /// <summary>
         /// An object to hold reusable <see cref="OpenApiCallback"/> Objects.
         /// </summary>
-        public virtual IDictionary<string, OpenApiCallback> Callbacks { get; set; } = new Dictionary<string, OpenApiCallback>();
+        public virtual IDictionary<string, OpenApiCallback>? Callbacks { get; set; } = new Dictionary<string, OpenApiCallback>();
 
         /// <summary>
         /// An object to hold reusable <see cref="OpenApiPathItem"/> Object.
         /// </summary>
-        public virtual IDictionary<string, OpenApiPathItem> PathItems { get; set; } = new Dictionary<string, OpenApiPathItem>();
+        public virtual IDictionary<string, OpenApiPathItem>? PathItems { get; set; } = new Dictionary<string, OpenApiPathItem>();
 
         /// <summary>
         /// This object MAY be extended with Specification Extensions.
         /// </summary>
-        public virtual IDictionary<string, IOpenApiExtension> Extensions { get; set; } = new Dictionary<string, IOpenApiExtension>();
+        public virtual IDictionary<string, IOpenApiExtension>? Extensions { get; set; } = new Dictionary<string, IOpenApiExtension>();
 
         /// <summary>
         /// Parameter-less constructor
@@ -118,7 +118,7 @@ public void SerializeAsV31(IOpenApiWriter writer)
             // pathItems - only present in v3.1
             writer.WriteOptionalMap(
             OpenApiConstants.PathItems,
-            PathItems,
+            PathItems!,
             (w, key, component) =>
             {
                 if (component.Reference != null &&
@@ -170,7 +170,7 @@ private void SerializeInternal(IOpenApiWriter writer, OpenApiSpecVersion version
             // schemas
             writer.WriteOptionalMap(
                 OpenApiConstants.Schemas,
-                Schemas,
+                Schemas!,
                 (w, key, s) =>
                 {
                     var reference = s.GetRef();
@@ -188,7 +188,7 @@ private void SerializeInternal(IOpenApiWriter writer, OpenApiSpecVersion version
             // responses
             writer.WriteOptionalMap(
                 OpenApiConstants.Responses,
-                Responses,
+                Responses!,
                 (w, key, component) =>
                 {
                     if (component.Reference != null &&
@@ -206,7 +206,7 @@ private void SerializeInternal(IOpenApiWriter writer, OpenApiSpecVersion version
             // parameters
             writer.WriteOptionalMap(
                 OpenApiConstants.Parameters,
-                Parameters,
+                Parameters!,
                 (w, key, component) =>
                 {
                     if (component.Reference != null &&
@@ -224,7 +224,7 @@ private void SerializeInternal(IOpenApiWriter writer, OpenApiSpecVersion version
             // examples
             writer.WriteOptionalMap(
                 OpenApiConstants.Examples,
-                Examples,
+                Examples!,
                 (w, key, component) =>
                 {
                     if (component.Reference != null &&
@@ -242,7 +242,7 @@ private void SerializeInternal(IOpenApiWriter writer, OpenApiSpecVersion version
             // requestBodies
             writer.WriteOptionalMap(
                 OpenApiConstants.RequestBodies,
-                RequestBodies,
+                RequestBodies!,
                 (w, key, component) =>
                 {
                     if (component.Reference != null &&
@@ -261,7 +261,7 @@ private void SerializeInternal(IOpenApiWriter writer, OpenApiSpecVersion version
             // headers
             writer.WriteOptionalMap(
                 OpenApiConstants.Headers,
-                Headers,
+                Headers!,
                 (w, key, component) =>
                 {
                     if (component.Reference != null &&
@@ -279,7 +279,7 @@ private void SerializeInternal(IOpenApiWriter writer, OpenApiSpecVersion version
             // securitySchemes
             writer.WriteOptionalMap(
                 OpenApiConstants.SecuritySchemes,
-                SecuritySchemes,
+                SecuritySchemes!,
                 (w, key, component) =>
                 {
                     if (component.Reference != null &&
@@ -297,7 +297,7 @@ private void SerializeInternal(IOpenApiWriter writer, OpenApiSpecVersion version
             // links
             writer.WriteOptionalMap(
                 OpenApiConstants.Links,
-                Links,
+                Links!,
                 (w, key, component) =>
                 {
                     if (component.Reference != null &&
@@ -315,7 +315,7 @@ private void SerializeInternal(IOpenApiWriter writer, OpenApiSpecVersion version
             // callbacks
             writer.WriteOptionalMap(
                 OpenApiConstants.Callbacks,
-                Callbacks,
+                Callbacks!,
                 (w, key, component) =>
                 {
                     if (component.Reference != null &&
@@ -331,7 +331,7 @@ private void SerializeInternal(IOpenApiWriter writer, OpenApiSpecVersion version
                 });
 
             // extensions
-            writer.WriteExtensions(Extensions, version);
+            writer.WriteExtensions(Extensions!, version);
             writer.WriteEndObject();
         }
 
@@ -343,7 +343,7 @@ private void RenderComponents(IOpenApiWriter writer, OpenApiSpecVersion version)
             {
                 writer.WriteOptionalMap(
                    OpenApiConstants.Schemas,
-                   Schemas,
+                   Schemas!,
                    (w, key, s) => { w.WriteJsonSchema(s, version); });
             }
             writer.WriteEndObject();