Non required argument

Hello, I have a simple function that contains an argument that is not required, ie: function list_formvars($pmatch) {... However, if I call the function without the argument, I get a warning (I'm having the app show all warnings for development): "Warning: Missing argument 1 for list_formvars(), called in ..." Though the function works fine, how would I go about then making argument not required. I've tried using an if statement with an isset() condition, but perhaps I don't have the syntax correct? Anyway, TIA for your comments. Donovan -- D Brooke