Error when build war file

config/warble.rb

@@ -1,4 +1,4 @@
-# frozen_string_literal: true
+
 
 Warbler::Config.new do |config|
   # Don't use gemjar, it seems it makes Gem load paths leak outside of the war
@@ -21,20 +21,26 @@
   config.jar_name = 'killbill-admin-ui-standalone'
 end
 
-module FixInit
+class Warbler::Jar
   def add_init_file(config)
-    super
-    return unless @files[config.init_filename]
-
-    contents = @files[config.init_filename].read
-    add_before = "require 'bundler/shared_helpers'"
-    line_to_add = "Gem.paths = ENV\n"
-    @files[config.init_filename] = StringIO.new(contents.gsub(add_before, "#{line_to_add}\\0"))
-  end
-end
-
-module Warbler
-  class Jar
-    prepend FixInit
+    if config.init_contents
+      contents = ''
+      config.init_contents.each do |file|
+        if file.respond_to?(:read)
+          contents << file.read
+        elsif File.extname(file) == '.erb'
+          contents << expand_erb(file, config).read
+        else
+          contents << File.read(file)
+        end
+      end
+      @files[config.init_filename] = StringIO.new(contents)
+    end
+    if @files[config.init_filename]
+      contents = @files[config.init_filename].read
+      add_before = "require 'bundler/shared_helpers'"
+      line_to_add = "Gem.paths = ENV\n"
+      @files[config.init_filename] = StringIO.new(contents.gsub(add_before, "#{line_to_add}\\0"))
+    end
   end
 end