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.

mcp/src/test/java/io/modelcontextprotocol/client/AbstractMcpSyncClientTests.java の testCallTool と、247 行目付近にあるそのアサーションから始めてください。everything server の成功レスポンスも確認してください。成功した結果で isError() is false が assert され、everything server が null ではなく false を返せば完了です。