//var %a $null | echo -a $encode(test,mcrl,%a)
//var %a $null | echo -a $encode(test,me,%a)
both keys are same as if the key 0x00 hex is used
//var %a $null | echo -a $encode(test,mcr,%a)
key derived from binary digest of $md5($null)
//var %a $null | echo -a $encode(test,mcs,%a,SaltSalt)
key derived from binary digest of $md5($null $+ SaltSalt)