Step regexp regression in v6 when value is empty

[fmagaldea]

Context

• Cucumber version: 6.0.5
• Node version: 13.1.0,
• Operating system: macOS 10.13.3 / same on circleci image node 13.1.0

Notice

This may be an issue on cucumber-expression, but I'm not sure.

Description

With cucumber-js version 5.1.0, the regexp ([^"]*) was detected as an empty string if in the feature file it was empty.
As of version 6, it's null.

Example

1. Let's define the step:

const {When} = require('cucumber');

When(/^The value equals "([^"]*)"$/, async function(value) {
  console.log(value);
});

2. Let's call the step:
   The value equals ""
3. The console output is:
   null
   whereas it should just log an empty string.

[bailejl]

We have the same issue. Our steps with "" use to return an empty string in the step, now we get null. Based on the Cucumber docs, we should get an empty string, link below.

Our version of Cucumber is 6.0.5.

https://cucumber.io/docs/cucumber/cucumber-expressions/#parameter-types

[pciruzzi]

Hi! We have a similar issue with the new cucumber version 6, which was working on 5.1.0. We had an step definition:

Given(/^(?:there are )?the following "([^"]+)" entities( on "([^"]+)" database)?:$/, function expectEntities(
  entityName,
  databaseName,
  entities,
)

Before, when using it like:

Given the following "foo" entities:

databaseName was undefined, but now it's giving a null. This is particularly messing things up, because we were relying on that parameter to call a function which has a default value. Now, as it's getting null instead of undefined, it's trying to use null instead of the default value.