Variable in select

Question

I have the following Linq to Entity Framework query:

//Get type strings from language depended resource file
string personTypeString = StaticHelpers.GetResourceString("TypeLabel.Person");
string companyTypeString = StaticHelpers.GetResourceString("TypeLabel.Company");

IQueryable<PersonCompany> query = Em.Persons.Select(p => new PersonCompany
                        {
                            DateOfBirth = p.DATE_OF_BIRTH,
                            Name = p.LAST_NAME + " " + p.FIRST_NAME,
                            TaxVatNr = null,
                            CustomerType = personTypeString
                        })
                .Concat( //union all
                    Em.Companies.Select(c => new PersonCompany
                        {
                            DateOfBirth = null,
                            Name = c.NAME,
                            TaxVatNr = c.TAX_VAT_NR,
                            CustomerType = companyTypeString
                        }));

When I try to execute the query I get the following error form the database:

ERROR [42610] [IBM][DB2/LINUXX8664] SQL0418N The statement was not processed because the statement contains an invalid use of one of the following: an untyped parameter marker, the DEFAULT keyword, or a null value.

The problematic part is Type = personTypeString because in the generated SQL it is replaced with @p__linq__0 as C4.
DB2 expects that the type of this parameter marker to be defined. In SQL you would write it as CAST(@p__linq__0 as VARCHAR(10)) AS C4.

How can I modify my linq query in a way that the generated SQL statement is executed correctly?

Note: The type of query must stay IQueryable<PersonCompany>.

EDIT: Here is the sql query generated by the entity framework:

SELECT 
Project3.C1 AS C1, 
Project3.C5 AS C5, 
Project3.C6 AS C6, 
Project3.C7 AS C7, 
Project3.C8 AS C8
FROM ( SELECT Project3.C1 AS C1, Project3.C5 AS C5, Project3.C6 AS C6, Project3.C7 AS C7, Project3.C8 AS C8, row_number() OVER (ORDER BY Project3.C6 ASC) AS row_number
    FROM ( SELECT 
        UnionAll1.C1 AS C1,
        UnionAll1.DATE_OF_BIRTH AS C5, 
        UnionAll1.C2 AS C6, 
        UnionAll1.C3 AS C7, 
        UnionAll1.C4 AS C8
        FROM  (SELECT 
            CAST(1 AS int) AS C1, 
            Extent1.DATE_OF_BIRTH AS DATE_OF_BIRTH, 
            Concat(Concat(Extent1.LAST_NAME, ' '), CASE WHEN (Extent1.FIRST_NAME IS NULL) THEN '' ELSE Extent1.FIRST_NAME END) AS C2, 
            CAST(NULL AS varchar(45)) AS C3, 
            @p__linq__0 AS C4
            FROM PPMS.PERSON AS Extent1
        UNION ALL
            SELECT 
            CAST(1 AS int) AS C1, 
            CAST(NULL AS timestamp) AS C2, 
            Extent2.NAME AS NAME, 
            Extent2.TAX_VAT_NR AS TAX_VAT_NR, 
            @p__linq__1 AS C3
            FROM PPMS.COMPANY AS Extent2) AS UnionAll1(C1, ID, CRE_DATE, CRE_USER, DATE_OF_BIRTH, C2, C3, C4, UPD_DATE, UPD_USER)
    )  AS Project3
)  AS Project3
WHERE Project3.row_number > 0
ORDER BY Project3.C6 ASC FETCH  FIRST 200 ROWS ONLY 

As I already mentioned, the problem is that there is no type defined for @p__linq__0.

The PersonCompany class is a simple class containing the properties. As @JunaidKirkire requested here is the code for PersonCompany:

public class PersonCompany
{
    private string _name;
    private string _custormerType;
    private DateTime? _dateOfBirth;
    private string _taxVatNr;

    public string Name
    {
        get { return _name; }
        set
        {
            if (_name == value) return;
            _name = value;
            OnPropertyChanged("Name");
        }
    }

    public string CustomerType
    {
        get { return _custormerType; }
        set
        {
            if (_custormerType == value) return;
            _custormerType = value;
            OnPropertyChanged("CustomerType");
        }
    }

    public DateTime? DateOfBirth
    {
        get { return _dateOfBirth; }
        set
        {
            if (_dateOfBirth == value) return;
            _dateOfBirth = value;
            OnPropertyChanged("DateOfBirth");
        }
    }

    public string TaxVatNr
    {
        get { return _taxVatNr; }
        set
        {
            if (_taxVatNr == value) return;
            _taxVatNr = value;
            OnPropertyChanged("TaxVatNr");
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    public void OnPropertyChanged(string propertyName)
    {
        if(PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}