Function picker_key 

pub fn picker_key(
    picker: &mut PickerState,
    multi: bool,
    event: &KeyEvent,
) -> PickerKey

What event does in an open picker: type to narrow, ↑↓ move, Space chooses (or toggles in a list of several), Enter chooses, Esc closes the picker only. In a pick-one list Space chooses only while the filter is empty, and types a space once it narrows, so a name of several words can be typed; with nothing typed it would match nothing and blank the list under the key that opened it.