What is the default behavior when you don't configure a terminating action in a security policy?

This should be the expected behavior in such scenario:

[edit security policies from-zone trust to-zone untrust policy default-permit]

root@vsrx1# show

match {

  source-address any;

  destination-address any;

  application any;

}

then {

  log {

    session-init;

  }

  ## Warning: missing mandatory statement(s): 'deny' or 'reject' or 'permit'

}

[edit security policies from-zone trust to-zone untrust policy default-permit]

root@vsrx1# commit check

[edit security policies from-zone trust to-zone untrust policy default-permit]

 'then'

  Missing mandatory statement: 'deny' or 'reject' or 'permit'

error: configuration check-out failed: (missing mandatory statements)

As you can see, you should receive a warning message and then a commit check error.