Fix Java SDK's sampling example

Signed-off-by: Dariusz Jędrzejczyk <[email protected]>

Author: chemicL

sdk/java/mcp-server.mdx

@@ -447,7 +447,8 @@ var calculatorTool = new McpServerFeatures.SyncToolSpecification(
 
         // Create a sampling request
         McpSchema.CreateMessageRequest request = McpSchema.CreateMessageRequest.builder()
-            .content(new McpSchema.TextContent("Calculate: " + arguments.get("expression")))
+            .messages(List.of(new McpSchema.SamplingMessage(McpSchema.Role.USER,
+                new McpSchema.TextContent("Calculate: " + arguments.get("expression")))
             .modelPreferences(McpSchema.ModelPreferences.builder()
                 .hints(List.of(
                     McpSchema.ModelHint.of("claude-3-sonnet"),