TypeScript Version: 3.5.2

Search Terms: undefined, function arguments, variable, if condition, static code analysis

Code

const foo = (bar: number) => {};

const someOtherFunction = (bar?: number) => {
  const shouldCallFoo = !!bar;

  if (shouldCallFoo) {
    foo(bar);
  }
}

Expected behavior:

The code compiles without any problems

Actual behavior:

Error:

Argument of type 'number | undefined' is not assignable to parameter of type 'number'.
  Type 'undefined' is not assignable to type 'number'.

Playground Link: http://www.typescriptlang.org/play/#code/MYewdgzgLgBAZiEMC8MAUAjAhgJwFwxgCuAthgKY4CUKAfDAN4C+A3AFBuiSwQgnkB5KAAtKAMSJhgUAJbgU6bDgD8BYmUo1k9Bmxj6YXaDAjCQRADYATAMJYLFsYgVL2egzLjpT563YdOIDS6BqHwiJi4VOyhTGxMQA

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