I use VS 2012 from project VS 2015 in vb.net there is an error

is there a best solution without error so I can use it in visual studio 2012?

thanks

'error cannot be converted to 'String' and The '?' character cannot be used here
For Each item In data
                lst.Add(New Session() With {
                    .SessionId = item,
                    .CustomerName = Order.GetCustomer(item)?.Name,
                    .Customer = Order.GetCustomer(item),
                    .TotalPrice = Order.GetTotal(item),
                    .CreatedAt = Order.GetDate(item)
                })
'error Overload resolution failed because no accessible 'Single' can be called with these arguments:
    Extension method 'Public Function Single(Of T)(expression As ServiceStack.OrmLite.ISqlExpression) As T' defined in 'ServiceStack.OrmLite.OrmLiteReadExpressionsApi': Type parameter 'T' cannot be inferred.
    Extension method 'Public Function Single(Of T)(expression As ServiceStack.OrmLite.SqlExpression(Of T)) As T' defined in 'ServiceStack.OrmLite.OrmLiteReadExpressionsApi': Type parameter 'T' cannot be inferred.
    Extension method 'Public Function Single(Of T)(predicate As System.Linq.Expressions.Expression(Of System.Func(Of T, Boolean))) As T' defined in 'ServiceStack.OrmLite.OrmLiteReadExpressionsApi': Type parameter 'T' cannot be inferred.
    Extension method 'Public Function Single(Of T)(sql As String, [anonType As Object = Nothing]) As T' defined in 'ServiceStack.OrmLite.OrmLiteReadApi': Type parameter 'T' cannot be inferred.
    Extension method 'Public Function Single(Of T)(anonType As Object) As T' defined in 'ServiceStack.OrmLite.OrmLiteReadApi': Type parameter 'T' cannot be inferred.
Public Shared Function GetDate(ByVal sessionId As String) As DateTime
            Return Db.Get().Single(Function(r) r.SessionId = sessionId).CreatedAt
        End Function
'error Operands of type Object used for operator '+'
item.Quantity += 1