Adds defensive programming

src/Microsoft.OpenApi/Models/OpenApiCallback.cs

@@ -45,10 +45,10 @@ public OpenApiCallback() { }
         /// </summary>
         public OpenApiCallback(OpenApiCallback callback)
         {
-            PathItems = new(callback.PathItems);
-            UnresolvedReference = callback.UnresolvedReference;
-            Reference = new(callback.Reference);
-            Extensions = new Dictionary<string, IOpenApiExtension>(callback.Extensions);
+            PathItems = callback?.PathItems != null ? new(callback?.PathItems) : null;
+            UnresolvedReference = callback?.UnresolvedReference ?? UnresolvedReference;
+            Reference = callback?.Reference != null ? new(callback?.Reference) : null;
+            Extensions = callback?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(callback.Extensions) : null;
         }
 
         /// <summary>

src/Microsoft.OpenApi/Models/OpenApiComponents.cs

@@ -78,16 +78,16 @@ public OpenApiComponents() { }
         /// </summary>
         public OpenApiComponents(OpenApiComponents components)
         {
-            Schemas = new Dictionary<string, OpenApiSchema>(components.Schemas);
-            Responses = new Dictionary<string, OpenApiResponse>(components.Responses);
-            Parameters = new Dictionary<string, OpenApiParameter>(components.Parameters);
-            Examples = new Dictionary<string, OpenApiExample>(components.Examples);
-            RequestBodies = new Dictionary<string, OpenApiRequestBody>(components.RequestBodies);
-            Headers = new Dictionary<string, OpenApiHeader>(components.Headers);
-            SecuritySchemes = new Dictionary<string, OpenApiSecurityScheme>(components.SecuritySchemes);
-            Links = new Dictionary<string, OpenApiLink>(components.Links);
-            Callbacks = new Dictionary<string, OpenApiCallback>(components.Callbacks);
-            Extensions = new Dictionary<string, IOpenApiExtension>(components.Extensions);
+            Schemas = components?.Schemas != null ? new Dictionary<string, OpenApiSchema>(components.Schemas) : null;
+            Responses = components?.Responses != null ? new Dictionary<string, OpenApiResponse>(components.Responses) : null;
+            Parameters = components?.Parameters != null ? new Dictionary<string, OpenApiParameter>(components.Parameters) : null;
+            Examples = components?.Examples != null ? new Dictionary<string, OpenApiExample>(components.Examples) : null;
+            RequestBodies = components?.RequestBodies != null ? new Dictionary<string, OpenApiRequestBody>(components.RequestBodies) : null;
+            Headers = components?.Headers != null ? new Dictionary<string, OpenApiHeader>(components.Headers) : null;
+            SecuritySchemes = components?.SecuritySchemes != null ? new Dictionary<string, OpenApiSecurityScheme>(components.SecuritySchemes) : null;
+            Links = components?.Links != null ? new Dictionary<string, OpenApiLink>(components.Links) : null;
+            Callbacks = components?.Callbacks != null ? new Dictionary<string, OpenApiCallback>(components.Callbacks) : null;
+            Extensions = components?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(components.Extensions) : null;
         }
 
         /// <summary>

src/Microsoft.OpenApi/Models/OpenApiContact.cs

@@ -45,10 +45,10 @@ public OpenApiContact() { }
         /// </summary>
         public OpenApiContact(OpenApiContact contact)
         {
-            Name = contact.Name;
-            Url = new Uri(contact.Url.OriginalString);
-            Email = contact.Email;
-            Extensions = new Dictionary<string, IOpenApiExtension>(contact.Extensions);
+            Name = contact?.Name ?? Name;
+            Url = contact?.Url != null ? new Uri(contact.Url.OriginalString) : null;
+            Email = contact?.Email ?? Email;
+            Extensions = contact?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(contact.Extensions) : null;
         }
 
         /// <summary>

src/Microsoft.OpenApi/Models/OpenApiDiscriminator.cs

@@ -32,8 +32,8 @@ public OpenApiDiscriminator() { }
         /// </summary>
         public OpenApiDiscriminator(OpenApiDiscriminator discriminator)
         {
-            PropertyName = discriminator.PropertyName;
-            Mapping = new Dictionary<string, string>(discriminator.Mapping);
+            PropertyName = discriminator?.PropertyName ?? PropertyName;
+            Mapping = discriminator?.Mapping != null ? new Dictionary<string, string>(discriminator.Mapping) : null;
         }
 
         /// <summary>

src/Microsoft.OpenApi/Models/OpenApiDocument.cs

@@ -72,15 +72,15 @@ public OpenApiDocument() {}
         /// </summary>
         public OpenApiDocument(OpenApiDocument document)
         {
-            Workspace = new(document.Workspace);
-            Info = new(document.Info);
-            Servers = new List<OpenApiServer>(document.Servers);
-            Paths = new(document.Paths);
-            Components = new(document.Components);
-            SecurityRequirements = new List<OpenApiSecurityRequirement>(document.SecurityRequirements);
-            Tags = new List<OpenApiTag>(document.Tags);
-            ExternalDocs = new(document.ExternalDocs);
-            Extensions = new Dictionary<string, IOpenApiExtension>(document.Extensions);
+            Workspace = document?.Workspace != null ? new(document?.Workspace) : null;
+            Info = document?.Info != null ? new(document?.Info) : null;
+            Servers = document?.Servers != null ? new List<OpenApiServer>(document.Servers) : null;
+            Paths = document?.Paths != null ? new(document?.Paths) : null;
+            Components = document?.Components != null ? new(document?.Components) : null;
+            SecurityRequirements = document?.SecurityRequirements != null ? new List<OpenApiSecurityRequirement>(document.SecurityRequirements) : null;
+            Tags = document?.Tags != null ? new List<OpenApiTag>(document.Tags) : null;
+            ExternalDocs = document?.ExternalDocs != null ? new(document?.ExternalDocs) : null;
+            Extensions = document?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(document.Extensions) : null;
         }
 
         /// <summary>

src/Microsoft.OpenApi/Models/OpenApiEncoding.cs

@@ -63,12 +63,12 @@ public OpenApiEncoding() {}
         /// </summary>
         public OpenApiEncoding(OpenApiEncoding encoding)
         {
-            ContentType = encoding.ContentType;
-            Headers = new Dictionary<string, OpenApiHeader>(encoding.Headers);
-            Style = encoding.Style;
-            Explode = encoding.Explode;
-            AllowReserved = encoding.AllowReserved;
-            Extensions = new Dictionary<string, IOpenApiExtension>(encoding.Extensions);
+            ContentType = encoding?.ContentType ?? ContentType;
+            Headers = encoding?.Headers != null ? new Dictionary<string, OpenApiHeader>(encoding.Headers) : null;
+            Style = encoding?.Style ?? Style;
+            Explode = encoding?.Explode ?? Explode;
+            AllowReserved = encoding?.AllowReserved ?? AllowReserved;
+            Extensions = encoding?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(encoding.Extensions) : null;
         }
 
         /// <summary>

src/Microsoft.OpenApi/Models/OpenApiExample.cs

@@ -64,13 +64,13 @@ public OpenApiExample() {}
         /// </summary>
         public OpenApiExample(OpenApiExample example)
         {
-            Summary = example.Summary;
-            Description = example.Description;
-            Value = OpenApiAnyCloneHelper.CloneFromCopyConstructor(example.Value);
-            ExternalValue = example.ExternalValue;
-            Extensions = new Dictionary<string, IOpenApiExtension>(example.Extensions);
-            Reference = new(example.Reference);
-            UnresolvedReference = example.UnresolvedReference;
+            Summary = example?.Summary ?? Summary;
+            Description = example?.Description ?? Description;
+            Value = OpenApiAnyCloneHelper.CloneFromCopyConstructor(example?.Value);
+            ExternalValue = example?.ExternalValue ?? ExternalValue;
+            Extensions = example?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(example.Extensions) : null;
+            Reference = example?.Reference != null ? new(example?.Reference) : null;
+            UnresolvedReference = example?.UnresolvedReference ?? UnresolvedReference;
         }
 
         /// <summary>

src/Microsoft.OpenApi/Models/OpenApiExternalDocs.cs

@@ -39,9 +39,9 @@ public OpenApiExternalDocs() {}
         /// </summary>
         public OpenApiExternalDocs(OpenApiExternalDocs externalDocs)
         {
-            Description = externalDocs.Description;
-            Url = new Uri(externalDocs.Url.OriginalString);
-            Extensions = new Dictionary<string, IOpenApiExtension>(externalDocs.Extensions);
+            Description = externalDocs?.Description ?? Description;
+            Url = externalDocs?.Url != null ? new Uri(externalDocs.Url.OriginalString) : null;
+            Extensions = externalDocs?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(externalDocs.Extensions) : null;
         }
 
         /// <summary>

src/Microsoft.OpenApi/Models/OpenApiHeader.cs

@@ -96,20 +96,20 @@ public OpenApiHeader() {}
         /// </summary>
         public OpenApiHeader(OpenApiHeader header)
         {
-            UnresolvedReference = header.UnresolvedReference;
-            Reference = new(header.Reference);
-            Description = header.Description;
-            Required = header.Required;
-            Deprecated = header.Deprecated;
-            AllowEmptyValue = header.AllowEmptyValue;
-            Style = header.Style;
-            Explode = header.Explode;
-            AllowReserved = header.AllowReserved;
-            Schema = new(header.Schema);
-            Example = OpenApiAnyCloneHelper.CloneFromCopyConstructor(header.Example);
-            Examples = new Dictionary<string, OpenApiExample>(header.Examples);
-            Content = new Dictionary<string, OpenApiMediaType>(header.Content);
-            Extensions = new Dictionary<string, IOpenApiExtension>(header.Extensions);
+            UnresolvedReference = header?.UnresolvedReference ?? UnresolvedReference;
+            Reference = header?.Reference != null ? new(header?.Reference) : null;
+            Description = header?.Description ?? Description;
+            Required = header?.Required ?? Required;
+            Deprecated = header?.Deprecated ?? Deprecated;
+            AllowEmptyValue = header?.AllowEmptyValue ?? AllowEmptyValue;
+            Style = header?.Style ?? Style;
+            Explode = header?.Explode ?? Explode;
+            AllowReserved = header?.AllowReserved ?? AllowReserved;
+            Schema = header?.Schema != null ? new(header?.Schema) : null;
+            Example = OpenApiAnyCloneHelper.CloneFromCopyConstructor(header?.Example);
+            Examples = header?.Examples != null ? new Dictionary<string, OpenApiExample>(header.Examples) : null;
+            Content = header?.Content != null ? new Dictionary<string, OpenApiMediaType>(header.Content) : null;
+            Extensions = header?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(header.Extensions) : null;
         }
 
         /// <summary>

src/Microsoft.OpenApi/Models/OpenApiInfo.cs

@@ -59,13 +59,13 @@ public OpenApiInfo() {}
         /// </summary>
         public OpenApiInfo(OpenApiInfo info)
         {
-            Title = info.Title;
-            Description = info.Description;
-            Version = info.Version;
-            TermsOfService = info.TermsOfService;
-            Contact = new(info.Contact);
-            License = new(info.License);
-            Extensions = new Dictionary<string, IOpenApiExtension>(info.Extensions);
+            Title = info?.Title ?? Title;
+            Description = info?.Description ?? Description;
+            Version = info?.Version ?? Version;
+            TermsOfService = info?.TermsOfService ?? TermsOfService;
+            Contact = info?.Contact != null ? new(info?.Contact) : null;
+            License = info?.License != null ? new(info?.License) : null;
+            Extensions = info?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(info.Extensions) : null;
         }
 
         /// <summary>

src/Microsoft.OpenApi/Models/OpenApiLicense.cs

@@ -39,9 +39,9 @@ public OpenApiLicense() {}
         /// </summary>
         public OpenApiLicense(OpenApiLicense license)
         {
-            Name = license.Name;
-            Url = new Uri(license.Url.OriginalString);
-            Extensions = new Dictionary<string, IOpenApiExtension>(license.Extensions);
+            Name = license?.Name ?? Name;
+            Url = license?.Url != null ? new Uri(license.Url.OriginalString) : null;
+            Extensions = license?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(license.Extensions) : null;
         }
 
         /// <summary>

src/Microsoft.OpenApi/Models/OpenApiLink.cs

@@ -71,15 +71,15 @@ public OpenApiLink() {}
         /// </summary>
         public OpenApiLink(OpenApiLink link)
         {
-            OperationRef = link.OperationRef;
-            OperationId = link.OperationId;
-            Parameters = new(link.Parameters);
-            RequestBody = new(link.RequestBody);
-            Description = link.Description;
-            Server = new(link.Server);
-            Extensions = new Dictionary<string, IOpenApiExtension>(link.Extensions);
-            UnresolvedReference = link.UnresolvedReference;
-            Reference = new(link.Reference);
+            OperationRef = link?.OperationRef ?? OperationRef;
+            OperationId = link?.OperationId ?? OperationId;
+            Parameters = link?.Parameters != null ? new(link?.Parameters) : null;
+            RequestBody = link?.RequestBody != null ? new(link?.RequestBody) : null;
+            Description = link?.Description ?? Description;
+            Server = link?.Server != null ? new(link?.Server) : null;
+            Extensions = link?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(link.Extensions) : null;
+            UnresolvedReference = link?.UnresolvedReference ?? UnresolvedReference;
+            Reference = link?.Reference != null ? new(link?.Reference) : null;
         }
 
         /// <summary>

src/Microsoft.OpenApi/Models/OpenApiMediaType.cs

@@ -53,11 +53,11 @@ public OpenApiMediaType() {}
         /// </summary>
         public OpenApiMediaType(OpenApiMediaType mediaType)
         {
-            Schema = new(mediaType.Schema);
-            Example = OpenApiAnyCloneHelper.CloneFromCopyConstructor(mediaType.Example);
-            Examples = new Dictionary<string, OpenApiExample>(mediaType.Examples);
-            Encoding = new Dictionary<string, OpenApiEncoding>(mediaType.Encoding);
-            Extensions = new Dictionary<string, IOpenApiExtension>(mediaType.Extensions);
+            Schema = mediaType?.Schema != null ? new(mediaType?.Schema) : null;
+            Example = OpenApiAnyCloneHelper.CloneFromCopyConstructor(mediaType?.Example);
+            Examples = mediaType?.Examples != null ? new Dictionary<string, OpenApiExample>(mediaType.Examples) : null;
+            Encoding = mediaType?.Encoding != null ? new Dictionary<string, OpenApiEncoding>(mediaType.Encoding) : null;
+            Extensions = mediaType?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(mediaType.Extensions) : null;
         }
 
         /// <summary>

src/Microsoft.OpenApi/Models/OpenApiOAuthFlow.cs

@@ -51,11 +51,11 @@ public OpenApiOAuthFlow() {}
         /// </summary>
         public OpenApiOAuthFlow(OpenApiOAuthFlow oAuthFlow)
         {
-            AuthorizationUrl = new Uri(oAuthFlow.AuthorizationUrl.OriginalString);
-            TokenUrl = new Uri(oAuthFlow.TokenUrl.OriginalString);
-            RefreshUrl = new Uri(oAuthFlow.RefreshUrl.OriginalString);
-            Scopes = new Dictionary<string, string>(oAuthFlow.Scopes);
-            Extensions = new Dictionary<string, IOpenApiExtension>(oAuthFlow.Extensions);
+            AuthorizationUrl = oAuthFlow?.AuthorizationUrl != null ? new Uri(oAuthFlow.AuthorizationUrl.OriginalString) : null;
+            TokenUrl = oAuthFlow?.TokenUrl != null ? new Uri(oAuthFlow.TokenUrl.OriginalString) : null;
+            RefreshUrl = oAuthFlow?.RefreshUrl != null ? new Uri(oAuthFlow.RefreshUrl.OriginalString) : null;
+            Scopes = oAuthFlow?.Scopes != null ? new Dictionary<string, string>(oAuthFlow.Scopes) : null;
+            Extensions = oAuthFlow?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(oAuthFlow.Extensions) : null;
         }
 
         /// <summary>

src/Microsoft.OpenApi/Models/OpenApiOAuthFlows.cs

@@ -49,11 +49,11 @@ public OpenApiOAuthFlows() {}
         /// <param name="oAuthFlows"></param>
         public OpenApiOAuthFlows(OpenApiOAuthFlows oAuthFlows)
         {
-            Implicit = new(oAuthFlows.Implicit);
-            Password = new(oAuthFlows.Password);
-            ClientCredentials = new(oAuthFlows.ClientCredentials);
-            AuthorizationCode = new(oAuthFlows.AuthorizationCode);
-            Extensions = new Dictionary<string, IOpenApiExtension>(oAuthFlows.Extensions);
+            Implicit = oAuthFlows?.Implicit != null ? new(oAuthFlows?.Implicit) : null;
+            Password = oAuthFlows?.Password != null ? new(oAuthFlows?.Password) : null;
+            ClientCredentials = oAuthFlows?.ClientCredentials != null ? new(oAuthFlows?.ClientCredentials) : null;
+            AuthorizationCode = oAuthFlows?.AuthorizationCode != null ? new(oAuthFlows?.AuthorizationCode) : null;
+            Extensions = oAuthFlows?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(oAuthFlows.Extensions) : null;
         }
 
         /// <summary>

src/Microsoft.OpenApi/Models/OpenApiOperation.cs

@@ -116,19 +116,19 @@ public OpenApiOperation() {}
         /// </summary>
         public OpenApiOperation(OpenApiOperation operation)
         {
-            Tags = new List<OpenApiTag>(operation.Tags);
-            Summary = operation.Summary;
-            Description = operation.Description;
-            ExternalDocs = new(operation.ExternalDocs);
-            OperationId = operation.OperationId;
-            Parameters = new List<OpenApiParameter>(operation.Parameters);
-            RequestBody = new(operation.RequestBody);
-            Responses = new(operation.Responses);
-            Callbacks = new Dictionary<string, OpenApiCallback>(operation.Callbacks);
-            Deprecated = operation.Deprecated;
-            Security = new List<OpenApiSecurityRequirement>(operation.Security);
-            Servers = new List<OpenApiServer>(operation.Servers);
-            Extensions = new Dictionary<string, IOpenApiExtension>(operation.Extensions);
+            Tags = new List<OpenApiTag>(operation?.Tags);
+            Summary = operation?.Summary ?? Summary;
+            Description = operation?.Description ?? Description;
+            ExternalDocs = operation?.ExternalDocs != null ? new(operation?.ExternalDocs) : null;
+            OperationId = operation?.OperationId ?? OperationId;
+            Parameters = operation?.Parameters != null ? new List<OpenApiParameter>(operation.Parameters) : null;
+            RequestBody = new(operation?.RequestBody);
+            Responses = operation?.Responses != null ? new(operation?.Responses) : null;
+            Callbacks = operation?.Callbacks != null ? new Dictionary<string, OpenApiCallback>(operation.Callbacks) : null;
+            Deprecated = operation?.Deprecated ?? Deprecated;
+            Security = operation?.Security != null ? new List<OpenApiSecurityRequirement>(operation.Security) : null;
+            Servers = operation?.Servers != null ? new List<OpenApiServer>(operation.Servers) : null;
+            Extensions = operation?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(operation.Extensions) : null;
         }
 
         /// <summary>