Object properties are returning null value that should not do so

[MovGP0]

Describe the bug
Currenty many properties are null by default that should have a default value that is not null.

The best practice is that properties shold return default values/objects that can be used instead of returning null values. The user should still be able to provide custom implementations of the objects if needed.

To Reproduce
Example when setting up McpServerOptions. The following code throws an Object reference not set to an instance of an object exception:

	McpServerOptions options = new()
	{
		ServerInfo =
		{
			Name = "MyServer",
			Version = "1.0.0"
		},
		Capabilities = {
			Tools = {
                            // ...
			}
		}
	};

Problem description

This behavior forces users to create new instances of the objects:

	McpServerOptions options = new()
	{
		ServerInfo = new()
		{
			Name = "MyServer",
			Version = "1.0.0"
		},
		Capabilities = new() {
			Tools = new() {
                            ListChanged = true,
                            ToolCollection = new() {
                                // ...
                             }
			}
		}
	};

Also, every time the user want to access the properties, a lot of null checks are required:

// current behavior
var handler = options.Capabilities?.Tools?.ListToolsHandler;

// expected behavior
var handler = options.Capabilities.Tools.ListToolsHandler;

Expected behavior

• Properties should provide default objects that can readily be used.
• Users should be able to set the values of the properties to other object instances

[MovGP0]

Another example:

Current Behavior

.AddMcpServer(opts =>
{
	opts.ServerInfo = new()
	{
		Name = "MyServer",
		Version = "1.0.0"
	};
})

Expected Behavior

.AddMcpServer(opts =>
{
	opts.ServerInfo.Name = "MyServer";
	opts.ServerInfo.Version = "1.0.0";
})

[stephentoub]

The best practice is that properties shold return default values/objects that can be used instead of returning null values. The user should still be able to provide custom implementations of the objects if needed.

These properties are nullable. It is not a best practice to have property getters lazily initialize objects when the property is nullable.

Also, every time the user want to access the properties, a lot of null checks are required:

These objects reflect the MCP protocol, which has these objects as optional, and it's important to know whether they were sent or not. When a server sends its capabilities to the client, for example, whether Tools is null or non-null states whether the server supports the tools capability; if we were to manufacture a non-null object on demand, that important information would be lost.

[MovGP0]

These properties are nullable.

My argument is that they shouldn't be nullable in the first place.

the MCP protocol, which has these objects as optional

This could also be handeled using an IsPristine or IsModified flag that gets set when any of the properties change their values. Ignoring properties with default values (ie. properties of type string with value string.Empty) might also work.

[stephentoub]

These properties are nullable.

My argument is that they shouldn't be nullable in the first place.

We disagree then. There is significant value in modeling these protocol-level types as they are modeled in the protocol itself.