def body(value)
      each_message_type do |_, message|
        next if message.nil?
        message.body = value
      end
    end
def body(value)
      each_message_type do |_, message|
        next if message.nil?
        message.body = value
      end
    end
Make a new message. Every message can be created using a hash,
 block, or direct assignment.

   message = Message.new do
     email do
       subject 'Subject'
     end
   end
   message = Message.new email: { subject: 'Subject' }
   message = Message.new
   message.email = Email.new subject: 'Subject'
 Loops through each registered message type and sets the content body.