OpenApiOperation copy constructor - RequestBody null not preserved

[dldl-cmd]

Describe the bug
OpenApiOperation copy constructor: public OpenApiOperation(OpenApiOperation operation) changes a null in the RequestBody into an object instance.

To Reproduce

var operation = new OpenApiOperation();
//operation.RequestBody = null is the default
var copiedOperation = new OpenApiOperation(operation);

copiedOperation.RequestBody is an new OpenApiRequestBody.

Expected behavior
copiedOperation.RequestBody should also be null, as on the source object.

OpenAPI.NET/src/Microsoft.OpenApi/Models/OpenApiOperation.cs

Lines 117 to 132 in db02b95

	public OpenApiOperation(OpenApiOperation operation)
	{
	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;
	}

I could provide a PR to fix this.

[MaggieKimani1]

@dldl-cmd please feel free to send a PR our way 🙂