fix contract on make-session

Allow `#:cookie-jar #f` as in docs and default.

Author: mflatt

http-easy-lib/http-easy/private/session.rkt

@@ -34,7 +34,7 @@
   [make-session (->* []
                      [#:pool-config pool-config?
                       #:ssl-context (or/c #f ssl-client-context? (promise/c ssl-client-context?))
-                      #:cookie-jar (is-a?/c cookie-jar<%>)
+                      #:cookie-jar (or/c #f (is-a?/c cookie-jar<%>))
                       #:proxies (listof proxy?)]
                      session?)]
   [session? (-> any/c boolean?)]

http-easy-test/net/http-easy/http-easy.rkt

@@ -424,6 +424,15 @@
    (test-suite
     "session"
 
+    (test-suite
+     "create"
+
+     (test-case "cookie jar can be #f"
+       (check-true (session? (make-session #:cookie-jar #f))))
+
+     (test-case "cookie jar cannot be a symbol"
+       (check-exn exn:fail:contract? (lambda () (make-session #:cookie-jar 'oops)))))
+
     (test-suite
      "breaks"