define explicitely that values should always be included in code completions

mcp-core/src/main/java/io/modelcontextprotocol/spec/McpSchema.java

@@ -2501,6 +2501,7 @@ public CompleteResult(CompleteCompletion completion) {
 		 * @param hasMore Indicates whether there are additional completion options beyond
 		 * those provided in the current response, even if the exact total is unknown
 		 */
+		@JsonInclude(JsonInclude.Include.ALWAYS)
 		public record CompleteCompletion( // @formatter:off
 				@JsonProperty("values") List<String> values,
 				@JsonProperty("total") Integer total,

mcp-core/src/test/java/io/modelcontextprotocol/spec/CompleteCompletionSerializationTest.java

@@ -0,0 +1,28 @@
+package io.modelcontextprotocol.spec;
+
+import io.modelcontextprotocol.json.McpJsonMapper;
+import org.junit.jupiter.api.Test;
+import java.io.IOException;
+import java.util.Collections;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class CompleteCompletionSerializationTest {
+
+	@Test
+	void codeCompletionSerialization() throws IOException {
+		McpJsonMapper jsonMapper = McpJsonMapper.getDefault();
+		McpSchema.CompleteResult.CompleteCompletion codeComplete = new McpSchema.CompleteResult.CompleteCompletion(
+				Collections.emptyList(), 0, false);
+		String json = jsonMapper.writeValueAsString(codeComplete);
+		String expected = """
+				{"values":[],"total":0,"hasMore":false}""";
+		assertEquals(expected, json, json);
+
+		McpSchema.CompleteResult completeResult = new McpSchema.CompleteResult(codeComplete);
+		json = jsonMapper.writeValueAsString(completeResult);
+		expected = """
+				{"completion":{"values":[],"total":0,"hasMore":false}}""";
+		assertEquals(expected, json, json);
+	}
+
+}