TypeScript can't parse optional object when assigned to a variable

[bnbarak]

TypeScript Version: 3.7.5

Code

type A = { b?:  { c?: number } }
const a: A = { b: {c: 123} };
const isSafe = a && a.b && a.b.c
// if (a && a.b && a.b.c) { // <= works
if (isSafe) { // <= breaks
    console.log(a.b.c); // (TS 2532) Object is possibly 'undefined'.
}

Expected behavior:
TS should check if isSafe protects against undefined
Actual behavior:
TS doesn't check isSafe

Output

"use strict";
const a = { b: { c: 123 } };
const isSafe = a && a.b && a.b.c;
// if (a && a.b && a.b.c) { // <= works
if (isSafe) { // <= breaks
    console.log(a.b.c); // (TS 2532) Object is possibly 'undefined'.
}

Compiler Options

{
  "compilerOptions": {
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictPropertyInitialization": true,
    "strictBindCallApply": true,
    "noImplicitThis": true,
    "noImplicitReturns": true,
    "useDefineForClassFields": false,
    "alwaysStrict": true,
    "allowUnreachableCode": false,
    "allowUnusedLabels": false,
    "downlevelIteration": false,
    "noEmitHelpers": false,
    "noLib": false,
    "noStrictGenericChecks": false,
    "noUnusedLocals": false,
    "noUnusedParameters": false,
    "esModuleInterop": true,
    "preserveConstEnums": false,
    "removeComments": false,
    "skipLibCheck": false,
    "checkJs": false,
    "allowJs": false,
    "declaration": true,
    "experimentalDecorators": false,
    "emitDecoratorMetadata": false,
    "target": "ES2017",
    "module": "ESNext"
  }
}

Playground Link: Provided

[nmain100]

Duplicate of #12184

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.