Bad assertion in testCallTool

In AbstractMcpSyncClientTests, there is a test case called {testCallTool](https://github.com/modelcontextprotocol/java-sdk/blob/110a8d1940ca2edf45524332dcc84b606e52d879/mcp/src/test/java/io/modelcontextprotocol/client/AbstractMcpSyncClientTests.java#L238)

on line 247 is this assertion:

			assertThat(result.isError()).isNull();

Although currently satisfied by the 'everything server' (assertion passes with javascript server) this assumes that the result.isError() (a Boolean value) is null if there is no error. Since 'isError() is set to 'false' and not null on success (by java server at least) this line should probably be:

			assertThat(result.isError()).isFalse();

and that the everything server should be fixed to return isError=false rather than isError=null as it does currently.

从 mcp/src/test/java/io/modelcontextprotocol/client/AbstractMcpSyncClientTests.java 中的 testCallTool 及其第 247 行附近的断言开始。也检查 everything server 的成功响应。完成的标准是：成功结果 assert isError() is false，并且 everything server 返回 false 而不是 null。