McpClient CallToolRequest arguments are received as null on the server side

[herbertkb]

I'm trying to create a very simple Spring AI MCP Server and am having trouble with a basic unit test.

@Component
public class CountEsTool {
    Logger log = LoggerFactory.getLogger(CountEsTool.class);

    @McpTool(name = "countEs", description = "Count the number of the letter 'e' in a word.")
    public int countEs(
            @McpToolParam(description = "word", required = true) String word) {
        log.info("word={}", word);

        int count = (int) List.of(word.split("")).stream()
                    .filter(s -> s.equalsIgnoreCase("e"))
                    .count();

        log.info("word={}, count={}", word, count);
        return count;
    }
}

If I run it with mvn spring-boot:run and test it with the MCP Inspector, it works fine.

But if I try to unit test it in the same way as shown in this blog
and this example,
the argument received on the server side in the tool method is null.

@Test
void toolResult() {

    var client = McpClient
            .sync(HttpClientStreamableHttpTransport.builder("http://localhost:" + port).build())
            .build();

    client.initialize();

    assertEquals(2, client.callTool(new CallToolRequest("countEs", Map.of("word", "elephant"))));

    client.closeGracefully();
}

com.example.reproducer.CountEsTool       : word=null

The reproducer repo for my problem is here: https://github.com/herbertkb/reproducer-spring-ai-mcp-server/tree/main

[wl2027]

@herbertkb enable maven compiler parameter names with <parameters>true</parameters> or -parameters