Avoid raising exception when target is nil

Author: Jesús Burgos

lib/rails-settings/setting_object.rb

@@ -87,7 +87,12 @@ def _target_class
     end
 
     def _setting?(method_name)
-      _target_class.setting_keys[var.to_sym][:default_value].keys.include?(method_name.to_s)
+      return false if target_id.nil? || target_type.nil?
+
+      _target_class
+        .setting_keys[var.to_sym][:default_value]
+        .keys
+        .include?(method_name.to_s)
     end
   end
 end