Yes / No project param in schedule

[Anonymous]

I took over a project where the issued sheets were being kept tract of using a Yes/No project parameter. Before it's Yes or No, it's blank. But once it's changes, it appears to have to be either Yes or No. Is there a way to reset the parameter to appear blank in the schedule?  Thanks.

[Alfredo_Medina · Accepted solution]

No. The initial value of yes/no parameter is "null". Once you activated with Yes, it can't go back to "null". 

[Anonymous]

That's what I was afraid of. I switched them to Text parameters. Thanks.