DynamicModel sample throws with EF8

[ajcvickers]

Unhandled exception. System.InvalidCastException: Unable to cast object of type 'System.String' to type 'System.Int32'.
   at lambda_method56(Closure, ValueBuffer)
   at System.Linq.Enumerable.SelectListIterator`2.MoveNext()
   at System.Linq.Enumerable.TryGetSingle[TSource](IEnumerable`1 source, Boolean& found)
   at lambda_method55(Closure)
   at Microsoft.EntityFrameworkCore.InMemory.Query.Internal.InMemoryQueryExpression.ResultEnumerable.GetEnumerator()
   at Microsoft.EntityFrameworkCore.InMemory.Query.Internal.InMemoryShapedQueryCompilingExpressionVisitor.QueryingEnumerable`1.Enumerator.MoveNextHelper()
   at Microsoft.EntityFrameworkCore.InMemory.Query.Internal.InMemoryShapedQueryCompilingExpressionVisitor.QueryingEnumerable`1.Enumerator.MoveNext()
   at System.Linq.Enumerable.TryGetSingle[TSource](IEnumerable`1 source, Boolean& found)
   at lambda_method54(Closure, QueryContext)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)
   at EFModeling.DynamicModel.Program.Main() in