Regular Expressions: Match Letters dot

I solved the challenge but have a question.

The challenge: Match all the letters in the string quoteSample.

My solution:

let quoteSample = "The quick brown fox jumps over the lazy dog.";
let alphabetRegex = /[a-z]/ig; // Change this line
let result = quoteSample.match(alphabetRegex); // Change this line

My question:

let alphabetRegex = /[a-z]./;

How come this throws an error? Doesn’t the dot match all letter cases?

What error does it throw?
Where are you seeing the error?
Can you post all the code you are using when you get the error?

Here’s the full code:

let quoteSample = "The quick brown fox jumps over the lazy dog.";
let alphabetRegex = /[a-z]./; // Change this line
let result = quoteSample.match(alphabetRegex); // Change this line

And the error message:

// running tests
Your regex alphabetRegex should match 35 items.
Cannot read property 'length' of null
Cannot read property 'length' of null
// tests completed