Inaccurate message returned for PUT request

Summary

The returned message for a PUT request to update the Epic Link custom field is not accurate. The request completes successfully but the message 204 No Content is returned.

Environment

Tested in JIRA 6.3.10 using Postman REST Client and cURL

Steps to Reproduce

1. Use Postman REST Client, send a PUT request to update Epic Link custom field
2. Use the following JSON data

   {
       "fields": {
          "customfield_10006": "SSP-24"
          }
   }
   

   10006 refers to the customfieldId for Epic Link; and SSP-24 is an Epic

Expected Results

Response code 200 (success)

Actual Results

204 No Content with "Malformed JSON" message