process.php returns content length of zero, causing error

[bagofarms]

this JavaScript error occurs after using UFIXIT:

Uncaught SyntaxError: Unexpected end of JSON input
    at JSON.parse (<anonymous>)
    at Object.success (default.js?cachebuster=1483561097:409)
    at j (jquery-2.1.1.min.js:2)
    at Object.fireWith [as resolveWith] (jquery-2.1.1.min.js:2)
    at x (jquery-2.1.1.min.js:4)
    at XMLHttpRequest.<anonymous> (jquery-2.1.1.min.js:4)

This has been traced back to process.php returning content with a length of zero. Here are the headers process.php returns:

HTTP/1.1 200 OK
Connection: keep-alive
Date: Wed, 04 Jan 2017 20:18:45 GMT
Server: Apache
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Content-Length: 0
Content-Type: text/html; charset=UTF-8
Via: 1.1 vegur