Initialize collections (lists, dictionaries) in the models (#96)

- Initialize all collection properties

- Remove default value from Info #85

- Ensure serializers to use Optional / Required writers correctly based on whether the property is marked as REQUIRED in the spec.

- Remove all "AddXXX" extensions except AddExtension, which is still useful in detecting badly formed names for extensions (e.g. not starting with x-)

- Fix unit tests

- Up nuget to 1.0.0-beta004

Author: PerthCharern

src/Microsoft.OpenApi.Readers/Microsoft.OpenApi.Readers.csproj

@@ -6,7 +6,7 @@
     <Company>Microsoft</Company>
     <Product>Microsoft.OpenApi.Readers</Product>
     <PackageId>Microsoft.OpenApi.Readers</PackageId>
-    <Version>1.0.0-beta003</Version>
+    <Version>1.0.0-beta004</Version>
     <Description>OpenAPI.NET Readers for JSON and YAML documents</Description>
     <AssemblyName>Microsoft.OpenApi.Readers</AssemblyName>
     <RootNamespace>Microsoft.OpenApi.Readers</RootNamespace>

src/Microsoft.OpenApi.Workbench/MainModel.cs

@@ -120,7 +120,7 @@ private string WriteContents(OpenApiDocument doc)
         {
             var outputstream = new MemoryStream();
             doc.Serialize(outputstream,
-                IsV3 ? OpenApiSpecVersion.OpenApi3_0 : OpenApiSpecVersion.OpenApi2_0,
+                IsV3 ? OpenApiSpecVersion.OpenApi3_0_0 : OpenApiSpecVersion.OpenApi2_0,
                 this.format == "Yaml" ? OpenApiFormat.Yaml : OpenApiFormat.Json);
 
             outputstream.Position = 0;

src/Microsoft.OpenApi/Extensions/OpenApiElementExtensions.cs

@@ -0,0 +1,47 @@
+// ------------------------------------------------------------
+//  Copyright (c) Microsoft Corporation.  All rights reserved.
+//  Licensed under the MIT License (MIT). See LICENSE in the repo root for license information.
+// ------------------------------------------------------------
+
+using Microsoft.OpenApi.Any;
+using Microsoft.OpenApi.Exceptions;
+using Microsoft.OpenApi.Interfaces;
+using Microsoft.OpenApi.Models;
+using Microsoft.OpenApi.Properties;
+
+namespace Microsoft.OpenApi.Extensions
+{
+    /// <summary>
+    /// Extension methods to verify validatity and add an extension to Extensions property.
+    /// </summary>
+    public static class OpenApiExtensibleExtensions
+    {
+        /// <summary>
+        /// Add extension into the Extensions
+        /// </summary>
+        /// <typeparam name="T"><see cref="IOpenApiExtensible"/>.</typeparam>
+        /// <param name="element">The extensible Open API element. </param>
+        /// <param name="name">The extension name.</param>
+        /// <param name="any">The extension value.</param>
+        public static void AddExtension<T>(this T element, string name, IOpenApiAny any)
+            where T : IOpenApiExtensible
+        {
+            if (element == null)
+            {
+                throw Error.ArgumentNull(nameof(element));
+            }
+
+            if (string.IsNullOrWhiteSpace(name))
+            {
+                throw Error.ArgumentNullOrWhiteSpace(nameof(name));
+            }
+
+            if (!name.StartsWith(OpenApiConstants.ExtensionFieldNamePrefix))
+            {
+                throw new OpenApiException(string.Format(SRResource.ExtensionFieldNameMustBeginWithXDash, name));
+            }
+
+            element.Extensions[name] = any ?? throw Error.ArgumentNull(nameof(any));
+        }
+    }
+}

src/Microsoft.OpenApi/Extensions/OpenApiExtensibleExtensions.cs

@@ -101,7 +101,7 @@ public static void Serialize<T>(this T element, IOpenApiWriter writer, OpenApiSp
 
             switch (specVersion)
             {
-                case OpenApiSpecVersion.OpenApi3_0:
+                case OpenApiSpecVersion.OpenApi3_0_0:
                     element.SerializeAsV3(writer);
                     break;
 

src/Microsoft.OpenApi/Extensions/OpenApiSerializableExtensions.cs

@@ -6,7 +6,7 @@
     <Company>Microsoft</Company>
     <Product>Microsoft.OpenApi</Product>
     <PackageId>Microsoft.OpenApi</PackageId>
-    <Version>1.0.0-beta003</Version>
+    <Version>1.0.0-beta004</Version>
     <Description>.NET models and JSON/YAML writers for OpenAPI specification</Description>
     <AssemblyName>Microsoft.OpenApi</AssemblyName>
     <RootNamespace>Microsoft.OpenApi</RootNamespace>

src/Microsoft.OpenApi/Microsoft.OpenApi.csproj

@@ -19,7 +19,8 @@ public class OpenApiCallback : IOpenApiSerializable, IOpenApiReferenceable, IOpe
         /// <summary>
         /// A Path Item Object used to define a callback request and expected responses. 
         /// </summary>
-        public Dictionary<RuntimeExpression, OpenApiPathItem> PathItems { get; set; }
+        public Dictionary<RuntimeExpression, OpenApiPathItem> PathItems { get; set; } 
+            = new Dictionary<RuntimeExpression, OpenApiPathItem>();
 
         /// <summary>
         /// Reference pointer.
@@ -29,7 +30,7 @@ public class OpenApiCallback : IOpenApiSerializable, IOpenApiReferenceable, IOpe
         /// <summary>
         /// This object MAY be extended with Specification Extensions.
         /// </summary>
-        public IDictionary<string, IOpenApiAny> Extensions { get; set; }
+        public IDictionary<string, IOpenApiAny> Extensions { get; set; } = new Dictionary<string, IOpenApiAny>();
 
         /// <summary>
         /// Add a <see cref="OpenApiPathItem"/> into the <see cref="PathItems"/>.