Handle null protocol version in the request

Author: adwsingh

mcp/mcp-server/src/main/java/software/amazon/smithy/java/mcp/server/McpServer.java

@@ -136,11 +136,13 @@ private void handleRequest(JsonRpcRequest req) {
                             pv = protocolVersion.identifier();
                         }
                     }
-
                     proxies.values().forEach(this::initialize);
+                    var builder = InitializeResult.builder();
+                    if (pv != null) {
+                        builder.protocolVersion(pv);
+                    }
                     writeResponse(req.getId(),
-                            InitializeResult.builder()
-                                    .protocolVersion(pv)
+                            builder
                                     .capabilities(Capabilities.builder()
                                             .tools(Tools.builder().listChanged(true).build())
                                             .prompts(Prompts.builder().listChanged(true).build())

mcp/mcp-server/src/test/java/software/amazon/smithy/java/mcp/server/McpServerTest.java

@@ -63,9 +63,18 @@ public void afterEach() {
     }
 
     private void initializeWithProtocolVersion(ProtocolVersion protocolVersion) {
-        write("initialize", Document.of(Map.of("protocolVersion", Document.of(protocolVersion.identifier()))));
+        final Document pvDoc;
+        final String expectedPv;
+        if (protocolVersion == null) {
+            pvDoc = Document.of(Map.of());
+            expectedPv = ProtocolVersion.v2024_11_05.INSTANCE.identifier();
+        } else {
+            pvDoc = Document.of(Map.of("protocolVersion", Document.of(protocolVersion.identifier())));
+            expectedPv = protocolVersion.identifier();
+        }
+        write("initialize", pvDoc);
         var pv = read().getResult().getMember("protocolVersion").asString();
-        assertEquals(protocolVersion.identifier(), pv);
+        assertEquals(expectedPv, pv);
     }
 
     @Test
@@ -116,7 +125,7 @@ public void validateToolsList() {
 
         server.start();
 
-        initializeWithProtocolVersion(ProtocolVersion.v2025_06_18.INSTANCE);
+        initializeWithProtocolVersion(null);
         write("tools/list", Document.of(Map.of()));
         var response = read();
         var result = response.getResult().asStringMap();