```ruby
module ApiVersions
  class Middleware
    def initialize(app)
      @app = app
    end

    def call(env)
      return @app.call(env) unless env['HTTP_ACCEPT']

      accepts = env['HTTP_ACCEPT'].split(',')
      offset = 0
      accepts.dup.each_with_index do |accept, i|
        accept.strip!
        match = /\Aapplication\/vnd\.#{ApiVersions::VersionCheck.vendor_string}\s*\+\s*(?<format>\w+)\s*/.match(accept)
        if match
          accepts.insert i + offset, "application/#{match[:format]}"
          offset += 1
        end
      end

      env['HTTP_ACCEPT'] = accepts.join(',')
      @app.call(env)
    end
  end
end
```

Allow for requests without headers to default to V1
user
```ruby
module ApiVersions
  class Middleware
    def initialize(app)
      @app = app
    end

    def call(env)
      return @app.call(env) unless env['HTTP_ACCEPT']
      env['HTTP_ACCEPT'] += ",application/vnd.#{ApiVersions::VersionCheck.vendor_string}+json" unless env['HTTP_ACCEPT'].include?(ApiVersions::VersionCheck.vendor_string)

      accepts = env['HTTP_ACCEPT'].split(',')
      offset = 0
      accepts.dup.each_with_index do |accept, i|
        accept.strip!
        match = /\Aapplication\/vnd\.#{ApiVersions::VersionCheck.vendor_string}\s*\+\s*(?<format>\w+)\s*/.match(accept)
        if match
          accepts.insert i + offset, "application/#{match[:format]}"
          offset += 1
        end
      end

      env['HTTP_ACCEPT'] = accepts.join(',')
      @app.call(env)
    end
  end
end
```
assistant