parse_content_type

# File actionpack/lib/action_dispatch/http/response.rb, line 410
    def parse_content_type(content_type)
      if content_type
        type, charset = content_type.split(/;\s*charset=/)
        type = nil if type && type.empty?
        ContentTypeHeader.new(type, charset)
      else
        NullContentTypeHeader
      end
    end