.ToSting() is not supported in Select

When selecting some value type that is needed to fill a string property, it throws an exception:

var itemsIntPropertiesAsString = items.Select(x => x.IntProperty.ToString()).ToList();

System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
at System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument argument, ExceptionResource resource)
at System.ThrowHelper.ThrowArgumentOutOfRangeException()
at System.SZArrayHelper.get_Item<T>(Int32 index)
at System.Collections.ObjectModel.ReadOnlyCollection`1.get_Item(Int32 index)
at NHibernate.Linq.Visitors.SelectArgumentsVisitor.VisitMethodCall(MethodCallExpression expr)
at NHibernate.Linq.Visitors.ExpressionVisitor.Visit(Expression exp)
at NHibernate.Linq.Visitors.NHibernateExpressionVisitor.Visit(Expression exp)
at NHibernate.Linq.Visitors.RootVisitor.HandleSelectCall(MethodCallExpression call)
at NHibernate.Linq.Visitors.RootVisitor.VisitMethodCall(MethodCallExpression expr)
at NHibernate.Linq.Visitors.ExpressionVisitor.Visit(Expression exp)
at NHibernate.Linq.Visitors.NHibernateExpressionVisitor.Visit(Expression exp)
at NHibernate.Linq.Visitors.NHibernateQueryTranslator.TranslateInternal(Expression expression)
at NHibernate.Linq.Visitors.NHibernateQueryTranslator.Translate(Expression expression, QueryOptions queryOptions)
at NHibernate.Linq.NHibernateQueryProvider.TranslateExpression(Expression expression)
at NHibernate.Linq.NHibernateQueryProvider.Execute(Expression expression)
at NHibernate.Linq.Query`1.GetEnumerator()