Revise #944 to avoid changing the API.

- ModMenu no longer displays a configuration icon for mods which implement the API but do not override `ModMenuApi.getModConfigScreenFactory()` (thanks `rcubedev`)
- This does not change the API

Author: gniftygnome

src/main/java/com/terraformersmc/modmenu/ModMenu.java

@@ -14,6 +14,7 @@
 import com.terraformersmc.modmenu.event.ModMenuEventHandler;
 import com.terraformersmc.modmenu.util.EnumToLowerCaseJsonConverter;
 import com.terraformersmc.modmenu.util.ModMenuScreenTexts;
+import com.terraformersmc.modmenu.util.NullScreenFactory;
 import com.terraformersmc.modmenu.util.UpdateCheckerUtil;
 import com.terraformersmc.modmenu.util.mod.Mod;
 import com.terraformersmc.modmenu.util.mod.fabric.FabricDummyParentMod;
@@ -103,9 +104,11 @@ public void onInitializeClient() {
 			String modId = metadata.getId();
 			try {
 				ModMenuApi api = entrypoint.getEntrypoint();
-                var factory = api.getModConfigScreenFactory();
-                if (factory != null) configScreenFactories.put(modId, factory);
-                apiImplementations.add(api);
+                ConfigScreenFactory<?> factory = api.getModConfigScreenFactory();
+                if (!(factory instanceof NullScreenFactory<?>)) {
+                    configScreenFactories.put(modId, factory);
+                }
+				apiImplementations.add(api);
 				updateCheckers.put(modId, api.getUpdateChecker());
 				providedUpdateCheckers.putAll(api.getProvidedUpdateCheckers());
 				api.attachModpackBadges(modpackMods::add);

src/main/java/com/terraformersmc/modmenu/api/ModMenuApi.java

@@ -2,7 +2,7 @@
 
 import com.terraformersmc.modmenu.ModMenu;
 import com.terraformersmc.modmenu.gui.ModsScreen;
-import org.jetbrains.annotations.Nullable;
+import com.terraformersmc.modmenu.util.NullScreenFactory;
 import net.minecraft.client.gui.screen.Screen;
 import net.minecraft.text.Text;
 
@@ -38,8 +38,8 @@ static Text createModsButtonText() {
 	 *
 	 * @return A factory for constructing config screen instances.
 	 */
-	default @Nullable ConfigScreenFactory<?> getModConfigScreenFactory() {
-		return null;
+	default ConfigScreenFactory<?> getModConfigScreenFactory() {
+		return new NullScreenFactory<>();
 	}
 
 	/**

src/main/java/com/terraformersmc/modmenu/util/NullScreenFactory.java

@@ -0,0 +1,15 @@
+package com.terraformersmc.modmenu.util;
+
+import com.terraformersmc.modmenu.api.ConfigScreenFactory;
+import net.minecraft.client.gui.screen.Screen;
+
+/*
+ * This class is used to detect mods which do not override the default ModMenuApi.getModConfigScreenFactory()
+ * while still preserving the guarantee the above API method does not return null.
+ */
+public class NullScreenFactory<S extends Screen> implements ConfigScreenFactory<S> {
+    @Override
+    public S create(Screen parent) {
+        return null;
+    }
+}