Fix null returned in Cucumber JSON scenario.description

[youtux]

Fix regression of #749 where we would serialize the scenario.description as null instead of the empty string.

[youtux]

@jsa34 FYI

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.08%. Comparing base (6cdd340) to head (2a3af16).
Report is 65 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #751   +/-   ##
=======================================
  Coverage   96.08%   96.08%           
=======================================
  Files          55       55           
  Lines        2250     2250           
  Branches      246      246           
=======================================
  Hits         2162     2162           
  Misses         53       53           
  Partials       35       35           

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[youtux]

It turns out there was no bug, only our Scenario and ScenarioTemplate typing is incorrect. Will fix them in #658