Fix a bug that error is raised when multi-line format

app/controllers/api_controller.rb

@@ -21,11 +21,14 @@ class ApiController < ApplicationController
   def regexp_preview
     preview = RegexpPreview.processor(params[:format]).new(params[:file], params[:format], params)
     matches = preview.matches
+
     render json: {
       params: {
         setting: {
-          regexp: preview.regexp.try(:source),
-          time_format: preview.time_format,
+          # NOTE: regexp and timeformat are used when format == 'apache' || 'nginx' || etc.
+          # TODO: prepare rendered JSON by prcessor(RegexpPreview::{Signle,Multi}Line
+          regexp: preview.try(:regexp).try(:source),
+          time_format: preview.try(:time_format),
         }
       },
       matches: matches.compact,