接受cmd中的空值.spec mow.cli

I took this code from mow.cli library A Larger Multi-Command Example https://github.com/jawher/mow.cli#spec. if my command is "config add "XX" -u="yname" -p="123"". the result is Adding account user:admin@XX But if I give a empty passphrase. Ex: "config add "XX" -u="yname" -p=" the program throws error.

Error: incorrect usage 

I see the cmd.Spec = "ACCOUNT [ -u= ] [ -p=]" is responsible for the input args. when I tried changing cmd.Spec = "ACCOUNT [ -u= ] [ -p=<>]" it does not work.

panic: Parse error at position 32:ACCOUNT [ -u=<username> ] [ -p=<>]

Is there any option where the program can accept a empty passphrase.

How about simply not passing the -p option ? i.e.:

config add XX -u=user