cucumber-expressions: returns undefined instead of empty string

[charlierudolph]

Summary

Reported in cucumber/cucumber-js#1241 that a cucumber-expressions of the form 'string {string} equals {string}' when matched against Given string "" equals "" returns undefined for the string values instead of empty strings.

Expected Behavior

When matching the cucumber-expression 'string {string} equals {string}' against the text Given string "" equals "", the values parsed should be empty strings.

Current Behavior

When matching the cucumber-expression 'string {string} equals {string}' against the text Given string "" equals "", the values parsed are each undefined.

Possible Solution

Not sure what changed but was working fine in previous versions. Its still matching correctly but for some reason isn't extracting a value

Steps to Reproduce (for bugs)

1. Linked to repo to reproduce: https://github.com/jbblanchet/cucumber-error
2. Clone repo
3. npm install
4. ./node_modules/.bin/cucumber-js

Context & Motivation

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