Rails 3.2 - mail not sending

I've got a mailer class in Rails 3.2 that refuses to send mail, giving the following error:

Outgoing message to devs: #<Mail::Message:98270300, Multipart: false, Headers: <From: no-reply@example.com>, <To: dev@example.com>, <Subject: Error with script>, <Mime-Version: 1.0>, <Content-Type: text/html>>

rake aborted!

At least one recipient (To, Cc or Bcc) is required to send a message

... yet the to field clearly has a recipient!

Here's my mailer class:

class Notifier < ActionMailer::Base
  def send_mail_to_developer(error)
    @error = error
    mail to: "dev@example.com", subject: "Error with script"
  end
end

Here's my rake task:

begin
  task :import_bars
    begin
      Foo.import_foos
    rescue => e
      mail = Notifier.mail_current_developers(error)
      puts "Outgoing message to devs: #{mail.inspect}"
      mail.deliver!
    end
  end
end

This seems just so curly so I'm not sure what to do or why this error is occurring. Help?