How to merge two IQueryable lists

I want to merge the records of two IQueryable lists in C#. I try

IQueryable<MediaType> list1 = values;
IQueryable<MediaType> list2 = values1;
obj.Concat(obj1);

and

IQueryable<MediaType> list1 = values;
IQueryable<MediaType> list2 = values1;
obj.Union(obj1);

but if list1 is empty then the resultant list is also empty. In my case either list1 can be empty but list2 can have records. How should i merge them?