Sequence contains no elements

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The error occurs when you try to access an object returned by a Linq query with 0 elements in the result set an
InvalidOperationException is thrown. Below is a simulation to generate the error:

Dim productQuery = From p In context.Products Where p.ID = -1 Select p

Dim p As Product = productQuery.Single()

An exception is thrown by the Single() method because the productQuery object has no products inside and the Single() method is
trying to reach the first entity in the productQuery.

To avoid this problem, we must check whether productQuery is containing some items or not. Here is the correct way to do it:

                                    Dim productQuery = From p In context.Products Where p.ID = -1 Select p 
                                    If productQuery.Count > 0 Then
                                            Dim p As Product = productQuery.Single()
                                    Else
                                            Return Nothing
                                    End If