Fix TypeError: Object.keys called on non-object

```
TypeError: Object.keys called on non-object
    at Function.keys (native)
    at Object.parseParameters (/home/cloud-user/did_groups_api/node_modules/newrelic/lib/util/urltils.js:78:14)
    at TraceSegment.markAsWeb (/home/cloud-user/did_groups_api/node_modules/newrelic/lib/transaction/trace/segment.js:91:32)
    at ServerResponse.instrumentedFinish (/home/cloud-user/did_groups_api/node_modules/newrelic/lib/instrumentation/core/http.js:127:15)
    at ServerResponse.g (events.js:199:16)
    at ServerResponse.<anonymous> (/home/cloud-user/did_groups_api/node_modules/newrelic/node_modules/continuation-local-storage/context.js:74:17)
    at ServerResponse.emit (events.js:129:20)
    at ServerResponse.emitted [as emit] (/home/cloud-user/did_groups_api/node_modules/newrelic/node_modules/continuation-local-storage/node_modules/emitter-listener/listener.js:122:21)
    at finish (_http_outgoing.js:517:10)
    at /home/cloud-user/did_groups_api/node_modules/newrelic/node_modules/continuation-local-storage/node_modules/async-listener/glue.js:188:31
```

At least in node 0.11.14, parsed.search is null, not an empty string when query is null:

```
parsed { protocol: null,
  hostname: null,
  slashes: null,
  hash: null,
  auth: null,
  search: null,
  host: null,
  query: null,
  port: null,
  pathname: '/favicon.ico',
  hostname: null,
  path: '/favicon.ico',
  hash: null,
  href: '/favicon.ico' }
  search: null,
  query: null,
  pathname: '/favicon.ico',
  path: '/favicon.ico',
  href: '/favicon.ico' }
```