InvalidCastException: Unable to cast object of type

public async Task<IActionResult> TestDashboard1()
    {
        var datasource = _context.ListingDTO_DBTable.AsQueryable();
        var query = datasource
            .Select(x => new ListingProjectsDTO() {
                Id = x.Id,
                ListingName = x.ListingName,
            });
         ConvertFromDBVal<string>(query);
        var listings = await query.ToListAsync();
        
        
        return View(listings);
    }
    
    public static T ConvertFromDBVal<T>(object obj)
    {
        if (obj == null || obj == DBNull.Value)
        {
            return default(T); 
        }
        else
        {
            return (T)obj; //InvalidCastException
        }
    }