Remote CAPTCHA bypass via None return

Incorrect return-value handling in Tethik flask-session-captcha before 1.2.1 allows remote attackers to bypass CAPTCHA checks via empty submissions. The captcha.validate() function returns None when given no value, while integrations that reject only an explicit False result treat that response as successful verification. Exploitation requires a Flask application using that comparison pattern; the consequence is bypass of the application's CAPTCHA gate and potentially the protected action, with no direct confidentiality or availability impact established.