C# IQueryable concatenate two fields after a group new

Question

I have this IQueryable that get some properties from my table, but it has a group new and I want to concatenate two string from there.

from comp in companies
join con in contacts on new { A = comp.Company_ID, B = comp.Location_ID } equals new { A = con.Company_ID, B = con.Location_ID } into comp_con
group new { comp, cc } by new
{
    comp.Company_ID,
    comp.Location_ID,
    comp.Company_Name,
    comp.City,
    comp.State,
    comp.Total_Fleet_Range,
    comp.Total_Locations
} into gcomp
select new MyObject
{
    ...,
    PropertyConcatenated = gcomp.Key.State + gcomp.Key.City // This is the part that doesn't work
};

When I try to make it a list, I got a null reference exception, but both the city and the state have values.