system76-firmware-dialog crashed with TypeError in loads(): the JSON object must be str, not 'NoneType'

[michaelcole]

Hey, I'm using Ubunu-GNOME and ran this command line after a failed update:

```
$ sudo /usr/lib/system76-driver/system76-firmware-dialog
[sudo] password for michael:
Traceback (most recent call last):
  File "/usr/lib/system76-driver/system76-firmware-dialog", line 560, in <module>
    data = json.loads(os.environ.get('FIRMWARE_DATA'))
  File "/usr/lib/python3.5/json/__init__.py", line 312, in loads
    s.__class__.__name__))
TypeError: the JSON object must be str, not 'NoneType'

```

ProblemType: Crash
DistroRelease: Ubuntu 16.04
Package: system76-driver 16.04.47 [origin: LP-PPA-system76-dev-stable]
ProcVersionSignature: Ubuntu 4.13.0-36.40~16.04.1-generic 4.13.13
Uname: Linux 4.13.0-36-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.15
Architecture: amd64
CrashDB: {'impl': 'launchpad', 'project': 'system76-driver'}
Date: Wed Mar 7 09:51:47 2018
ExecutablePath: /usr/lib/system76-driver/system76-firmware-dialog
InstallationDate: Installed on 2017-09-16 (171 days ago)
InstallationMedia: Ubuntu 16.04.3 LTS "Xenial Xerus" - Release amd64 (20170801)
InterpreterPath: /usr/bin/python3.5
PackageArchitecture: all
ProcCmdline: /usr/bin/python3 /usr/lib/system76-driver/system76-firmware-dialog
ProcEnviron:
 LANG=en_US.UTF-8
 TERM=xterm-256color
 PATH=(custom, no user)
 LC_CTYPE=en_US.UTF-8
 SHELL=/bin/bash
PythonArgs: ['/usr/lib/system76-driver/system76-firmware-dialog']
SourcePackage: system76-driver
Title: system76-firmware-dialog crashed with TypeError in loads(): the JSON object must be str, not 'NoneType'
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups:

[michaelcole (8-launchpad-michaelcole-com)]

See also https://bugs.launchpad.net/system76-driver/+bug/1754111