TS2454 Variable is used before being assigned with strictNullChecks when variable is clearly assigned but can be undefined

🔎 Search Terms

Variable is used before being assigned TS2454 TS(2454) undefined strictNullChecks

🕗 Version & Regression Information

• This happens at least since version 3.7.5 (tested in the playground)
• This is the behavior in every version I tried, and I reviewed the FAQ

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/DYUwLgBGIM6QvBArgOwCYgGYEsUjQNwBQR0cEiA5JRAIYwRwBOuA5hAD7Lpa77GlYYAPwA6UClZgAFgSA

💻 Code

let test = undefined;

test = '' as string | undefined;

test?.length; // Variable 'test' is used before being assigned.

🙁 Actual behavior

Typescript throws an error complaining about test being used before being assigned but it's clearly assigned to undefined and then to ''.

Mine is a very simplicistic problem, but the same issues happens if a replace '' with a call to a function.

🙂 Expected behavior

Typescript should assign the type string | undefined to the variable test and let me use it.

Additional information about the issue

No response