How to print NULL when table has no rows in SQL Server?

I have a table with a named column but no rows.

Col1

I wanted to write a select similar to:

SELECT TOP(1)
    NULLIF(Col1, '')
FROM table

I wanted to get a result like:

   Col1
1  NULL

But instead I get just the Col1 name and no results. How can I get a table with NULL as the result?

Answer

You can use aggregation:

    select max(col1)
    from t;

An aggregation query with no group by or having always returns one row. If there are no rows then the value is (generally) NULL for aggregation functions (the exception is COUNT()).