Unable to get SystemUser FullName in LINQ

Hi,

 I am unable to get the FullName,FirstName, LastName or YomiFullName of a SystemUser using LINQ query in plugin. All these have values in the SystemUserBase table.Below is the code

var createdList= from u1 in orgContext.SystemUserSet
where u1.Id == postAppt.CreatedBy.Id
select new
{
YomiFullName = u1.FullName,
FirstName = u1.FirstName,
LastName = u1.LastName,
InternalEMailAddress = u1.InternalEMailAddress
};
foreach (var cUser in createdList)
{
createdByUser = cUser.YomiFullName;
localContext.TracingService.Trace("cUser " + cUser.FullName+ " " + cUser.InternalEMailAddress + " " + cUser.LastName);
break;
}

Note : I am getting the value for InternalEMailAddress.