Expose Nullable / Nonnull on public properties / methods

Expected Behavior

Certain fields in MCP are mandatory, some are optional. I would expect to be able to know whether a certain property or function could be or return null from the Java SDK API.

Current Behavior

It is opaque to me what can be null or not.

Context

One example is CallToolResult, where isError() or Content.priority() are wrapped primitive types that can be null. However, since they don't have an @Nullable annotation, those facts are not obvious to the dev and can cause bugs (most notably null pointer exceptions).

首先检查与 CallToolResult.isError() 和 Content.priority() 相关的公共 Java SDK API，issue 指出它们虽然使用了包装的基本类型，但仍可能为 nullable。确定哪些公共属性和方法可以返回 null，然后验证它们的 nullability 是否通过注解明确公开，以便调用方能够识别 nullable 值。