add null check for modid when registering modmenu screens

omega-config-gui/src/main/java/draylar/omegaconfiggui/OmegaConfigGui.java

@@ -30,6 +30,8 @@ public class OmegaConfigGui {
      */
     public static <T extends Config> void registerConfigScreen(T config) {
         if(FabricLoader.getInstance().isModLoaded("modmenu")) {
+            // Ensure the config has a valid modid.
+            if(config.getModid() != null) {
                 OmegaScreenFactory<Screen> factory = OmegaConfigGui.getConfigScreenFactory(config);
 
                 if(modMenuInitialized) {
@@ -37,6 +39,9 @@ public class OmegaConfigGui {
                 } else {
                     REGISTERED_CONFIGURATIONS.put(config, factory);
                 }
+            } else {
+                OmegaConfig.LOGGER.warn(String.format("Skipping config screen registration for '%s' - you must implement getModid() in your config class!", config.getName()));
+            }
         }
     }