C# – The specified cast from a materialized ‘System.Int32’ type to the ‘System.Double’ type is not valid

When executing the following query, I get the error:

The specified cast from a materialized 'System.Int32' type to the
'System.Double' type is not valid.

var data = ctx.tblTO
                   .Where(m => m.Id == Id)
                   .GroupBy(m => m.EmployeeId)
                   .Select(m => new
                   {
                       workDay = m.Sum(k => k.WorkDay),
                       onDutyDay = m.Sum(k => k.OnDutyDay),
                       holiDay = m.Sum(k => k.Holiday)
                   })
                   .FirstOrDefault();

The datatype of WorkDay, OnDutyDay and Holiday is double. There is no Int32 here, so why do I get this error?

How can I solve this error?

public class TO
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }           
    public int EmployeeId { get; set; }
    public double WorkDay { get; set; }
    public double OnDutyDay { get; set; }
    public double Holiday { get; set; }
}