Function empty_tree_name 

pub fn empty_tree_name(object_format: &str) -> Option<&'static str>

What: The empty tree’s object name for an object format as git rev-parse --show-object-format spells it, or None for a format this table does not know. Why: None sends the caller to ask Git, so a future object format is answered by Git and never guessed here.

In TS you’d write (pseudocode):

function emptyTreeName(objectFormat: string): string | undefined;