Fix NPE causing crash when reporting a minimal error

[fractalwrench]

Goal

v4.16.1 added reporting of minimal error information, by encoding key information such as handled state in the filename. If the JSON payload was corrupted in any way, this means an incomplete report could be delivered with at least some information.

If an older corrupted report was cached on disk this would return a null error as the information was not encoded in the filename. This changeset adds a null check to prevent an NPE in the notify() call.

Tests

Added a mazerunner scenario that creates an empty file with an old filename that does not contain encoded information. The notifier should not generate a report from this file and should also not crash.

[bengourley]

Looks good, works as specified. I tested without your changeset and reproduced the problem. Testing with your changeset I could no longer reproduce the npe.

A couple of things to note:

1. when the app boots with a bad file, it outputs "sending 1 saved error" twice:

   07-23 14:50:58.197 27016 27033 I Bugsnag : Sending 1 saved error(s) to Bugsnag
   07-23 14:50:58.207 27016 27033 I Bugsnag : Sending 1 saved error(s) to Bugsnag
   07-23 14:50:58.263 27016 27016 I Bugsnag : Initialised NDK Plugin
   07-23 14:50:58.270 27016 27016 I Bugsnag : Initialised ANR Plugin
   07-23 14:50:58.778 27016 27033 I Bugsnag : Completed session tracking request
   

2. the offending file isn't removed from the device's filesystem

[fractalwrench]

the offending file isn't removed from the device's filesystem

I think this may be an issue with adb not synchronising the file directory, which we observed last time when testing the original minimal error implementation. The file is deleted here: https://github.com/bugsnag/bugsnag-android/pull/534/files#diff-5fcb9931669c81ccf180176a177f999eR180

I will investigate why that message shows up twice (and also make a small fix to the mazerunner tests)

[bengourley]

I think this may be an issue with adb not synchronising the file directory

I'm not sure about that… if repeatedly open/close the app (without making it crash again) it says this every time:

Sending 1 saved error(s) to Bugsnag
Sending 1 saved error(s) to Bugsnag

This suggests to me that the file isn't removed? (in addition to seeing it in the device file explorer)

[fractalwrench]

I've done the following testing:

• Added an empty file via the Device File Explorer named '"1504255147933_683c6b92-b325-4987-80ad-77086509ca1e.json", which did not send a minimal error report or crash the app
• Added a partial + empty file via adb on a rooted emulator, which sent a minimal error report without crashing the app.

In all cases the file was deleted after the app was launched, and I did not observe 'Sending 1 saved error(s) to Bugsnag' being displayed more than once at any point.

[bengourley]

I think this may be an issue with adb not synchronising the file directory

I'm not sure about that… if repeatedly open/close the app (without making it crash again) it says this every time:

Sending 1 saved error(s) to Bugsnag
Sending 1 saved error(s) to Bugsnag

This suggests to me that the file isn't removed? (in addition to seeing it in the device file explorer)

This was down to some weirdness with my emulator state. I tested on a different one (with a different api level) and it worked.

@fractalwrench tested on an emulator with the same api level as my weird on (26) and it also worked.