# TS1135: Argument expression expected.

> An argument list has an empty slot, as in `f(1, , 2)`. Fill it in or remove the extra comma.

## What it means

Each comma in a call's argument list must separate two expressions. Unlike array literals,
argument lists can't have holes.

## Example

```ts
export function f(a: number, b: number) { return a + b; }
f(1, , 2);
```

## How to fix

- Remove the extra comma, or pass a value (use `undefined` to skip an optional parameter).

Source: https://ts-r.dev/errors/TS1135/