Rails invalid byte sequence in UTF-8 when using htmlentities gem - ruby-on-rails

Question

So I have the controller who scrapes the entire html of a page and stores it into mysql database. Before I store the data I want to encode it using the htmlentities gem. My issue is that with some websites it works ok e.g https://www.lookagain.co.uk/ but with others I get invalid byte sequence in UTF-8 such as https://www.google.co.uk/ and I do not know why. At first I though it might be something wrong with the database so I have changed all the fields to LONGTEXT but the problem still persists
Controller:
class PageScraperController < ApplicationController
require 'nokogiri'
require 'open-uri'
require 'diffy'
require 'htmlentities'
def scrape
#url = watched_link_params[:url].to_s
puts "LOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOG#{#url}"
#page = Nokogiri::HTML(open(#url))
coder = HTMLEntities.new
#encodedHTML = coder.encode(#page)
create
end
def index
#savedHTML = ScrapedPage.all
end
def show
#savedHTML = ScrapedPage.find(id)
end
def new
#savedHTML = ScrapedPage.new
end
def create
#savedHTML = ScrapedPage.create(domain: #url, html: #encodedHTML, css: '', javascript: '')
if #savedHTML.save
puts "ADDED TO THE DATABASE"
redirect_to(root_path)
else
puts "FAILED TO ADD TO THE DATABASE"
end
end
def edit
end
def upadate
end
def delete
#watched_links = ScrapedPage.find(params[:id])
end
def destroy
#watched_links = ScrapedPage.find(params[:id])
#watched_links.destroy
redirect_to(root_path)
end
def watched_link_params
params.require(:default).permit(:url)
end
end