Why crontab is deleted when running on 'crontab' or 'crontab -' command with ctrl+D ?

Issue

• crontab replaces when running on crontab or crontab - with ctrl+D in stdin mode.

[test@localhost ~]$ crontab -l
* * * * * echo test 
[test@localhost ~]$ crontab
* * * * * /bin/test                      <----- Type rule and ctrl + D
[test@localhost ~]$ crontab -l
* * * * * /bin/test
[test@localhost ~]$ crontab -            <----- Type nothing and ctrl + D
[test@localhost ~]$ crontab -l
[test@localhost ~]$          # // empty