SSRS subreport parameter - multi values

Question

as you can see below, i need to pass a parameter value (red arrow) i tried to use this expression: =iif(Parameters!Country.Count = Parameters!CountryCount.Value, Nothing, Join(Parameters!Country.Value,",")) but im receiving an error when im try to run the report (Error: Subreport could not be shown.)

can you please assist and guide me how to pass multi value parameter? country - manually list i created (not from DB / SQL)

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If you pass nothing to your subreport, then how do you expect it to run and return something? Is your subreport allowed to run with nothing as a paramter? — Harry
As Harry mentioned, you would need the parameter's Allow Null value box to be checked in order for it to allow for the NOTHING. If the parameter is using Available values, NULL must be one of those Available values. — Hannover Fist