https://github.com/microsoft/TypeScript-Website/blame/0612591abc2d8292c8ddd084b5fb264f203b7026/packages/documentation/copy/en/declaration-files/Do's and Don'ts.md#L81
Sorry if this is overthinking - i am new to typescript.
You are giving a DO example with an interface called "Fetcher" that defines getObject but returning nothing aka void. I think I got the point of "Do write callback parameters as non-optional", but the context is somewhat unfortunate. Maybe there can be thought of a better example for non-optional callback parameters?
Another way to phrase my thought: Is it a DO to use return type void on a getter-Method?