Test for empty label

[Logerfo]

This test is useful, since it allows users to define empty labels, as the following:

merged: ''

Source.

Empty labels will not be added to/removed from the issue.

I did this because I want to use this bot only for the "opened" label.

The diff is weird if you don't pay enough attention to it, but all I did was enclose the promises with conditionals.

In draft stage because it tests are lacking.

[codecov]

Codecov Report

Merging #10 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #10   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           4      4           
  Lines          53     59    +6     
  Branches        5     11    +6     
=====================================
+ Hits           53     59    +6

Impacted Files	Coverage Δ
src/pull-handler.js	100% <100%> (ø)	⬆️

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[Logerfo]

@rsarky do you know how we could add unit tests for this cases? It needs to use a specific config file for each test.

[rsarky]

Hey @Logerfo. Sorry for the late response, busy with some course work atm.
This feature seems pretty useful, I will give the PR a look next weekend. Thanks for contributing 😄