Nullable default properties must have null default value instead of EmptyJsonObject

[nerzhulart]

Example

@Serializable
public data class ServerCapabilities(
    val experimental: JsonObject? = EmptyJsonObject,
    val sampling: JsonObject? = EmptyJsonObject,
    val logging: JsonObject? = EmptyJsonObject,
    val prompts: Prompts? = null,
    val resources: Resources? = null,
    val tools: Tools? = null,
) 

The default options for logging is EmptyJsonObject. When not specified (assuming no logging support on server) it effecively sends "logging" : {} that treated by a client as logging is supported