Output 400 rather than 500 error when Stash can't recognize/parse JSON objects properly

curl -v -H "Content-Type: application/json" -H "Accept: application/json" -u 'user:pass' -X POST --data-binary @data http://localhost:7990/rest/api/1.0/projects/LULU/repos/lulu/pull-requests

{
    \\"title\\": \\"Talking Nerdy\\",
    \\"description\\": \\"It’s a kludge, but put the tuple from the database in the cache.\\",
    \\"state\\": \\"OPEN\\",
    \\"open\\": true,
    \\"closed\\": false,
    \\"fromRef\\": {
        \\"id\\": \\"refs/heads/branch1\\",
        \\"repository\\": {
            \\"slug\\": \\"lulu\\",
            \\"name\\": null,
            \\"project\\": {
                \\"key\\": \\"LULU\\"
            }
        }
    },
    \\"toRef\\": {
        \\"id\\": \\"refs/heads/master\\",
        \\"repository\\": {
            \\"slug\\": \\"lulu\\",
            \\"name\\": null,
            \\"project\\": {
                \\"key\\": \\"LULU\\"
            }
        }
    },
    \\"reviewers\\": [
        {
            \\"user\\": {
                \\"name\\": \\"rluispereiramartins\\"
            }
        }
    ]
}

* Adding handle: conn: 0x7f8779803000
* Adding handle: send: 0
* Adding handle: recv: 0
* Curl_addHandleToPipeline: length: 1
* - Conn 0 (0x7f8779803000) send_pipe: 1, recv_pipe: 0
* About to connect() to localhost port 7990 (#0)
*   Trying ::1...
* Connected to localhost (::1) port 7990 (#0)
* Server auth using Basic with user 'rluispereiramartins'
> POST /rest/api/1.0/projects/LULU/repos/lulu/pull-requests HTTP/1.1
> Authorization: Basic cmx1aXNwZXJlaXJhbWFydGluczpybHVpc3BlcmVpcmFtYXJ0aW5z
> User-Agent: curl/7.30.0
> Host: localhost:7990
> Content-Type: application/json
> Accept: application/json
> Content-Length: 699
> 
* upload completely sent off: 699 out of 699 bytes
< HTTP/1.1 500 Internal Server Error
* Server Apache-Coyote/1.1 is not blacklisted
< Server: Apache-Coyote/1.1
< X-AREQUESTID: 719x160x0
< Set-Cookie: JSESSIONID=3E3411D8C461E65F73BAAD13877E5C55; Path=/; HttpOnly
< X-AUSERNAME: rluispereiramartins
< X-AUSERID: 1
< X-ASESSIONID: lrcpv6
< Cache-Control: no-cache, no-transform
< Vary: X-AUSERNAME,Accept-Encoding
< Transfer-Encoding: chunked
< Content-Type: application/json;charset=UTF-8
< X-Content-Type-Options: nosniff
< Date: Fri, 10 Jan 2014 10:59:40 GMT
< Connection: close
< 
* Closing connection 0
{"errors":[{"context":null,"message":"An error occurred while processing the request. Check the server logs for more information.","exceptionName":null}]}