How to get enumerable or collection of values from WhereSelectListIterator

I need to write a generic method for getting distinct values and propertyName is not known in advance. I want to do it using the LINQ expression. I am trying the below way but when getting the result from SelectMethod invoke I am getting WhereSelectListIterator. I want to convert it to IEnumerable so I can call the Distinct method. But I am not to cast it to IEnumerable(as it's not implemented it). How to get Enumerable back from WhereSelectListIterator or is there any way I can get IEnumerable directly from invoke of generic method.