How to clear a parameter in Mangle

RouterOS Scripting
1

I try to clear ‘per-connection-classifier’ paramter but seem there are nothing can help.
I can only clear the paramter via winbox, can not do that via ssh:
not work: ip firewall mangle set [/ip firewall mangle find comment=rule1] per-connection-classifier=
not work: ip firewall mangle set [/ip firewall mangle find comment=rule1] per-connection-classifier=“”
not work: ip firewall mangle set [/ip firewall mangle find comment=rule1] per-connection-classifier=none
Please help

2 
ip firewall mangle unset [/ip firewall mangle find comment=rule1] value-name=per-connection-classifier
3 
/ip firewall mangle set [find where comment="rule1"] !per-connection-classifier

or

/ip firewall mangle unset [find where comment="rule1"] per-connection-classifier