Seems have someone meet same problem with me:
https://emacs.stackexchange.com/questions/30857/clojure-code-evaluation-in-org-mode-produces-no-output

[stardiviner]           <Hack this world!>      GPG key ID: 47C32433
IRC(freeenode): stardiviner                     Twitter:  @numbchild
Key fingerprint = 9BAA 92BC CDDD B9EF 3B36  CB99 B8C4 B8E5 47C3 2433
Blog: http://stardiviner.github.io/

On Mon, Feb 20, 2017 at 8:41 PM, numbchild@gmail.com <numbchild@gmail.com>
wrote:

> ```
>       #+BEGIN_SRC clojure :session
>       (def kk "stardiviner")
>       #+END_SRC
> ```
>
> Press =[C-c C-c]= to evaluate this. Then check out =kk= in CIDER REPL
> buffer.
>
> That's why my problem happens:
>
> https://emacs.stackexchange.com/questions/30849/how-to-
> generate-inline-plot-result-for-ob-clojure
>
> Also I did some simple edebug on ob-clojure.el:
>
> =ob-clojure.el::org-babel-execute:clojure=
>
> ```
>       #+BEGIN_SRC emacs-lisp
>       (nrepl-dict-get
>        (nrepl-sync-request:eval "(print \"hello, world!\")"
> (cider-current-connection) (cider-current-session))
>        ;; key: "output", "status"
>        "output")
>       #+END_SRC
> ```
>
> ```
>        #+RESULTS:
>        #+BEGIN_EXAMPLE
>        (dict "status"
>              ("namespace-not-found" "done" "error" "done" "state" "state")
>              "id" "8" "session" "7dcda490-01d9-4411-a05b-804a4f8663b6"
> "changed-namespaces"
>              (dict)
>              "repl-type" "cljclj")
>        #+END_EXAMPLE
> ```
>
> You can see the request evaluate result is error.
>
>
> [stardiviner]           <Hack this world!>      GPG key ID: 47C32433
> IRC(freeenode): stardiviner                     Twitter:  @numbchild
> Key fingerprint = 9BAA 92BC CDDD B9EF 3B36  CB99 B8C4 B8E5 47C3 2433
> Blog: http://stardiviner.github.io/
>