The protected modifier for constructor should be enough.

Constructors of abstract classes can only be called in constructors of
their subclasses. So there is no point in making them public.

src/main/java/world/bentobox/bentobox/api/commands/admin/DefaultAdminCommand.java

@@ -30,7 +30,7 @@ public abstract class DefaultAdminCommand extends CompositeCommand {
      *
      * @param addon   - GameMode addon
      */
-    public DefaultAdminCommand(GameModeAddon addon) {
+    protected DefaultAdminCommand(GameModeAddon addon) {
         // Register command with alias from config.
         super(addon,
                 addon.getWorldSettings().getAdminCommandAliases().split(" ")[0],