bug/1676 fix graceful handling of "key not found" error for journey and event

[JoernBerkefeld]

PR details

What changes did you make? (Give an overview)

• closes [BUG] trying to retrieve a non-existing event key will break following retrieve-by-key events #1676

Further details (optional)

...

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• test scripts updated
• Wiki updated (if applicable)

[github-actions]

Coverage Report

Commit:04754c8
Base: develop@41a9454

Type	Base	This PR
Total Statements Coverage	69.83%	69.83%  (+0%)
Total Branches Coverage	68.71%	68.71%  (+0%)
Total Functions Coverage	81.55%	81.55%  (+0%)
Total Lines Coverage	69.83%	69.83%  (+0%)

Details (changed files):

File	Statements	Branches	Functions	Lines
lib/metadataTypes/Event.js	54.01%	37.31%	70%	54.01%
lib/metadataTypes/Journey.js	58.73%	60.91%	75%	58.73%