HMCL/src/main/java/org/jackhuang/hmcl/Metadata.java

@@ -165,11 +165,14 @@ public final class Metadata {
         return getClientFileApi() + "/server-manifest.json";
     }
 
+    /// Fallback join address when the installed modpack manifest has no `serverAddress` / routes.
+    public static final String DEFAULT_SERVER_ADDRESS = "mc.potatolab.uk";
+
     /// Server address used when the installed modpack manifest does not provide one.
     ///
-    /// Can be set at build or run time with the `hmcl.server.address` system property; empty by default.
+    /// Override at build or run time with `-Dhmcl.server.address=…`; defaults to [#DEFAULT_SERVER_ADDRESS].
     public static String getDefaultServerAddress() {
-        return System.getProperty("hmcl.server.address", "").trim();
+        return System.getProperty("hmcl.server.address", DEFAULT_SERVER_ADDRESS).trim();
     }
 
     /// The server name shown in the title bar.

HMCL/src/test/java/org/jackhuang/hmcl/game/ServerEndpointTest.java

@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: GPL-3.0-or-later WITH AdditionRef-HMCL
 package org.jackhuang.hmcl.game;
 
+import org.jackhuang.hmcl.Metadata;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
@@ -19,13 +20,15 @@ public final class ServerEndpointTest {
     }
 
     @Test
-    void noConfigurationMeansNoRoute(@TempDir Path dir) {
-        assertTrue(ServerEndpoint.routes(dir.resolve("modpack.json")).isEmpty());
-        assertNull(ServerEndpoint.selected(dir.resolve("modpack.json")));
+    void fallsBackToBakedDefaultAddress(@TempDir Path dir) {
+        var routes = ServerEndpoint.routes(dir.resolve("modpack.json"));
+        assertEquals(1, routes.size());
+        assertEquals(Metadata.DEFAULT_SERVER_ADDRESS, routes.get(0).address());
+        assertEquals(routes.get(0), ServerEndpoint.selected(dir.resolve("modpack.json")));
     }
 
     @Test
-    void fallsBackToDefaultAddress(@TempDir Path dir) {
+    void propertyOverridesBakedDefaultAddress(@TempDir Path dir) {
         System.setProperty("hmcl.server.address", " play.example.net:25565 ");
         var routes = ServerEndpoint.routes(dir.resolve("modpack.json"));
         assertEquals(1, routes.size());