fix: Attempt to provide some information for <unlabeled event>

[kamilogorek]

This one was very tricky to debug and fix. Some details and reasoning behind the fix.

First, there are 3 ways to trigger this issue, so let's go one by one:

captureException('');
captureMessage('');
throw '';

Before

captureException('')

There's no type and no message, as when a string is passed, it'll fallback to captureException. The thing why it's special is that we default to stracktrace: true and there's synthetic stack trace created by new Error('') which should help a user to debug the issue.

---

captureMessage('')

No type, no message, and no stack trace, as we default to false when using captureMessage directly :(

---

throw ''

No type, no message, no stack trace, and parse error on top of that :(

After

captureException('')

No changes.

---

captureMessage('')

We have a stack trace now \o/

---

throw ''

Overriden type. More reasonable message. No processing error and file, line and column of the main call \o/

FAQ

• Why it only affects ''?
  Because null and undefined coerce to their string representation and are valid labels

• Why can we not fix it using synthetic stack traces in TraceKit?
  Because by the time throw '' reaches global error handler, you cannot new Error('') it anymore. It has no data that can be fed to the constructor.

• Are there other ways around if once I find the culprit?
  Yes, you can use

Raven.wrap(function () {
   ...your code...
})

// or 

try {
  ...your code...
} catch (e) {
  // Synthetic stack traces are possible in `try/catch` clauses, even with `throw ''` calls
  const ex = new Error(e);
  Raven.captureException(ex);
}

Ref: #1271

[mitsuhiko]

WFM. This is an example of something where we might want to report to the relay a hint going forward that users should not do that :D

[codecov-io]

Codecov Report

Merging #1397 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #1397   +/-   ##
======================================
  Coverage    73.6%   73.6%           
======================================
  Files          31      31           
  Lines         701     701           
  Branches      104     104           
======================================
  Hits          516     516           
  Misses        182     182           
  Partials        3       3

---

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[victorpavlenko]

@HazAT pls merge

[glebmachine]

@HazAT please publish