ReplacingExpressionTreeVisitor does not deal with extension expressions correctly; this will cause ParameterExpressions to remain in the resolved predicates.
This is for symmetry with the MethodCallTransformerRegistries. Callers must now check the result for null before using it.
Support queries of the following forms:
Cooks.Select (c => (c.IsStarredCook ? c.LetterOfRecommendation : c.Name).Length) Cooks.Select (c => (c.FirstName ?? c.Name).Length)
Support for queries of the following form: from c in Cooks group c by c.Name into families where families.Count() > 1 select families.Key.
Queries that select grouping collections are not supported.