Today I ran into this error:

jj5@mercy:~/public-git$ git push origin master
error: gnutls_handshake() failed: A TLS warning alert has been received. while accessing https://demo@demo.personalserver.com/public/git/info/refs 

The solution, of all things, was to add a ServerName spec into my Apache configuration file /etc/apache2/sites-enabled/default-ssl.conf, e.g.:

ServerName demo.personalserver.com

Bug fixed!!