How to tell if an out parameter was set already?

Is there a way to know if an out parameter was set already or not. This is the pseudocode for what I am looking for:

public virtual string blabla(long num, out bool bval)
     {
         if (!bval.HasValue)
             {
             //Do some default logic
             bval = defaultValue;
             }
 
         return blabla2(num, bval);
     }
 

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