👓 What did you see?

This line:

can throw an uncaught exception in some circumstances

✅ What did you expect to see?

No exception

📦 Which tool/library version are you using?

Cucumber lang service 1.6.0

🔬 How could we reproduce it?

Go to live demo https://cucumber.github.io/monaco/

Delete the table. Now start a new doc string with 3 quotes. Your editor content will now be

@foo
Feature: Hello
Scenario: Hi
  Given I have 58 cukes in my belly
  And this is an undefined step
    """

Check the console. It contains this error

Uncaught TypeError: Cannot read properties of undefined (reading 'length')
    at t.getGherkinDiagnostics (getGherkinDiagnostics.js:67:52)
    at configureMonaco.js:96:58
    at configureMonaco.js:105:17

📚 Any additional context?

It seems like Monaco gives a line number 1 higher than the actual number of lines, in the case of EOF issues. So when indexing into lines, the result is undefined.