DEV: Manage edge case not custom fields

plugin.rb

@@ -239,7 +239,7 @@ after_initialize do
 
   on(:before_create_topic) do |topic_params, user|
     category = topic_params.category
-    wizard_submission_id = topic_params.custom_fields['wizard_submission_id']
+    wizard_submission_id = topic_params.custom_fields&.[]('wizard_submission_id')
     if category&.custom_fields&.[]('create_topic_wizard').present? && wizard_submission_id.blank?
       raise Discourse::InvalidParameters.new(
         I18n.t('wizard.error_messages.wizard_replacing_composer')