getLiteralParameterValue in a KPI formula

I would like to use a parameter value in a KPI in my API_Calculate business rule.

I have a literal value parameter and we will change the default value ahead of time to control which formula runs. I'm trying to pull the current default value with the following:

Dim param As String = BRApi.Dashboards.Parameters.GetLiteralParameterValue(si, False, Nothing, "myFlag")

When it gets to that line it throws a "Object reference not set to an instance of an object". 

Any ideas?