2nd crash on Heroku

[gideonthomas]

This brought down the heroku dyno as well:

20 Jul 2017 17:16:31.165 595 <190>1 2017-07-20T21:16:30.812615+00:00 host app web.1 - {"name":"openbadges-backpack","url":"/issuer.js","responseTime":7,"res":{"statusCode":304,"header":"HTTP/1.1 304 Not Modified\r\nX-Powered-By: Express\r\nStrict-Transport-Security: max-age=10886400000; includeSubDomains\r\nx-frame-options: DENY\r\naccess-control-allow-origin: *\r\netag: \"-1839928381\"\r\nDate: Thu, 20 Jul 2017 21:16:30 GMT\r\nConnection: close\r\n\r\n"},"msg":"Outgoing Response: HTTP 304 /issuer.js (7 ms)","time":"2017-07-20T21:16:30.807Z","v":0}
» 20 Jul 2017 17:16:31.733 727 <190>1 2017-07-20T21:16:31.523343+00:00 host app web.1 - {"name":"openbadges-backpack","err":{"message":"Cannot read property 'issuer' of null","name":"TypeError","stack":"TypeError: Cannot read property 'issuer' of null\n at getLinkedIssuer (/app/node_modules/openbadges-validator/index.js:271:36)\n at fn (/app/node_modules/openbadges-validator/node_modules/async/lib/async.js:582:34)\n at Object._onImmediate (/app/node_modules/openbadges-validator/node_modules/async/lib/async.js:498:34)\n at processImmediate [as _immediateCallback] (timers.js:363:15)"},"msg":"Cannot read property 'issuer' of null","time":"2017-07-20T21:16:31.523Z","v":0}
» 20 Jul 2017 17:16:31.812 58 <190>1 2017-07-20T21:16:31.523357+00:00 host app web.1 -
» 20 Jul 2017 17:16:31.812 95 <190>1 2017-07-20T21:16:31.523477+00:00 host app web.1 - /app/node_modules/messina/index.js:40
» 20 Jul 2017 17:16:31.812 74 <190>1 2017-07-20T21:16:31.523885+00:00 host app web.1 - throw err;
» 20 Jul 2017 17:16:31.813 71 <190>1 2017-07-20T21:16:31.523892+00:00 host app web.1 - ^
» 20 Jul 2017 17:16:31.813 106 <190>1 2017-07-20T21:16:31.523911+00:00 host app web.1 - TypeError: Cannot read property 'issuer' of null
» 20 Jul 2017 17:16:31.813 137 <190>1 2017-07-20T21:16:31.523912+00:00 host app web.1 - at getLinkedIssuer (/app/node_modules/openbadges-validator/index.js:271:36)
» 20 Jul 2017 17:16:31.813 147 <190>1 2017-07-20T21:16:31.523913+00:00 host app web.1 - at fn (/app/node_modules/openbadges-validator/node_modules/async/lib/async.js:582:34)
» 20 Jul 2017 17:16:31.813 164 <190>1 2017-07-20T21:16:31.523914+00:00 host app web.1 - at Object._onImmediate (/app/node_modules/openbadges-validator/node_modules/async/lib/async.js:498:34)
» 20 Jul 2017 17:16:31.813 124 <190>1 2017-07-20T21:16:31.523915+00:00 host app web.1 - at processImmediate [as _immediateCallback] (timers.js:363:15)