How to send a file with actionmailer 3.2.20?

Sending csv file with actionmailer-3.2.20, but getting the file with name noname with the text:

This is a multi-part message in MIME format...

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This is action mailer code

 def my_mail(file_path)
    attachments["file.csv"] = {mime_type: 'text/csv', content: File.read("file.csv")}
    mail(to: "mail@gmail.com", subject: "this is subject")
  end