Error when accessing to optional argument of overloaded function inside correct type guard

[jareguo]

TypeScript Version: 3.8.3

Search Terms: type guard function optional overload

Code

class MyClass {
    foo () {}
}

function add (test: number): void;
function add (test: object, paramIfObject: MyClass): void;  // should overload this declaration
function add (test: number | object, paramIfObject?: MyClass): void {
    if (typeof test === 'object') {  // Indicated the argument to overload is not optional
        paramIfObject.foo();   // Error: Object is possibly 'undefined'.(2532)
    }
}

Expected behavior: Compile successfully

Actual behavior: Error: Object is possibly 'undefined'.(2532)

Description: The variable paramIfObject was used inside the if statement, which should be a type guard refering to the correct function overload. So the variable should not compiled as an optional argument. Just equals to this: (no error)

Playground Link: Playground Link

Related Issues:

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"
  }
}

[RyanCavanaugh]

See #14515

[jareguo]

Thanks