Protect constructors from empty opts

[jonathantneal]

Which issue # if any, does this resolve?

There is a critical issue cloning nodes with children. The internal cloning function calls Node constructors without arguments, but those constructors require them. There were no tests for this. This PR:

1. Adds a test that triggers the existing error.
2. Fixes all affected constructors, causing the test to pass.

Please check one:

• New tests created for this change
• Tests updated for this change

---

Some Node constructors require an options argument that is an object (See https://github.com/shellscape/postcss-values-parser/blob/v1.5.0/lib/number.js#L7-L11)

class NumberNode extends Node {
  constructor (opts) {
    super(opts);
    this.type = 'number';
    this.unit = opts.unit || ''; // <- See that opts must present and an object
  }

However, the internal cloneNode function does pass any parameters to constructors (See https://github.com/shellscape/postcss-values-parser/blob/v1.5.0/lib/node.js#L4).

let cloned = new obj.constructor(); // <- See that nothing will be passed

Therefore, when cloning a parent node like rgb(255, 0, 0), this tool throws an error: Cannot read property 'unit' of undefined.

This error has been reported in one of my projects using postcss-values-parser: postcss/postcss-custom-properties#134

---

This PR allows Node constructors to work without an object.

Could this be slipped into a PATCH release?

[shellscape]

with Node 4 out of LTS (for some time now) we can accomplish this with a default parameter.

constructor(opts = {})

I know it's six of one, half dozen of another, but I'd rather have the moving in a forward direction there. any objections?

[jonathantneal]

Thanks for reviewing, @shellscape. I will make this change if this sole argument does not convince you:

Handling opts within the function means accidental arguments like new Comment(null) and new Comment(false) still work.

Handling opts within params means potentially getting errors like Cannot read property 'unit' of null, which may not be descriptive enough.

If you are unconvinced, let me know, and I will make the change within 5 minutes of your decision. 😄

[shellscape]

man, I'd hate to be the dev trying those wonky incantations, but you have a point.

[shellscape]

Cheers 🎉

[jonathantneal]

Thank you so much, @shellscape. May we have a 1.5.1 or 1.6.0 release for this?

According to the commit log @ https://github.com/shellscape/postcss-values-parser/commits/master we are still in PATCH status.

[shellscape]

When I get the chance to, yes.