Rails - render static html page from middleware

Question

Yesterday my application was visited by yandex bot with an invalid URL

/restday?biG%D9%02

and for this application is throwing an error

ArgumentError: invalid byte sequence in UTF-8

I need to render 400.html static page with status 400 instead of 404 whenever there is a invalid character error. I followed the solutions from this question and rack-robustness gem but it doesn't serve the purpose as it shows 404 or redirects to particular page.

I have added the following to /config/application.rb

require "#{Rails.root}/lib/handle_invalid_percent_encoding.rb"
config.middleware.insert 0, HandleInvalidPercentEncoding

And this is my middleware handle_invalid_percent_encoding.rb

require 'rack'

class HandleInvalidPercentEncoding

 def initialize(app)
   @app = app
 end

 def call(env)
   request = Rack::Request.new(env.dup)
   temp = request.params rescue :bad_form_data
   if temp == :bad_form_data
     error_response
   else
     @app.call(env)
   end
 end

 private

 def error_response
   # serve static html file
 end

end

P.S I need to render bad request error only when the argument error is Invalid encoding.