reCAPTCHA v2 fallback doesn't work when no referer header is sent

Expected behavior:ReCaptcha should respect the optional nature of the referer header. All versions of the captcha should load regardless of whether a referer header was sent.Observed behavior:Users with both Javascript and referrers disabled are greeted with an unhelpful error message:An error occurred: An internal error occurred: 51A929486E890.A4432E7.CD044181 -- You received this message because you are subscribed to the Google Groups "reCAPTCHA" group. To unsubscribe from this group and stop receiving emails from it, send an email to recaptcha+unsubscribe@googlegroups.com. To post to this group, send email to recaptcha@googlegroups.com. Visit this group at http://bit.ly/1dkFnYd. For more options, visit http://bit.ly/P65DvS.