Fix wrapping of null' when provided as Any'.

Reported by 'dingfeng' on #racket.
Please merge to 5.2.

original commit: da5b68fd4d944cef981062de5ed6d283a351fd1d

collects/tests/typed-racket/succeed/any-wrap-list.rkt

@@ -0,0 +1,11 @@
+#lang racket/load
+
+(module m typed/racket
+  (provide f)
+  (define: f : Any '(a (2 3))))
+
+(module n racket
+  (require 'm)
+  (list? (second f)))
+
+(require 'n)

collects/typed-racket/utils/any-wrap.rkt

@@ -7,12 +7,15 @@
   (lambda (v p write?)
     (fprintf p "#<Typed Value: ~a>" (any-wrap-val v))))
 
+(define undef (letrec ([x x]) x))
+
 (define (traverse wrap?)
   (define (t v)
     (match v
       [(? (lambda (e) (and (any-wrap? e) (not wrap?)))) (any-wrap-val v)]
       [(? (lambda (e)
             (or (number? e) (string? e) (char? e) (symbol? e)
+                (null? e) (regexp? e) (eq? undef e)
                 (keyword? e) (bytes? e) (boolean? e) (void? e))))
        v]
       [(cons x y) (cons (t x) (t y))]