Problem

[email protected]:

x = if a:
  if b: c

const x = a ? b ? c : void 0 : null;

If a is false, x === null, but if a is true and b is false, x === undefined; this is inconsistent with the defined behavior of IfExpressions which is to produce null when the alternate is omitted.

Cause

This:
https://github.com/lightscript/babel-plugin-lightscript/blob/eb650acf69a17f0e4af9ce10a4c1bdeacec1e9e7/src/index.js#L504
which leads to this:
https://github.com/babel/babel/blob/1e55653ac173c3a59f403a7b5269cf6d143d32d9/packages/babel-traverse/src/path/replacement.js#L195
which leads to this:
https://github.com/babel/babel/blob/master/packages/babel-types/src/converters.js#L47

Babel's algorithm for converting statements to expressions produces undefined by default.

Resolution

It is probably necessary to recapitulate this algorithm inside the lsc transform and make sure it makes nulls here.