# Description
`Expression::replace_in_variable` is only called in one place, and it is
called with `new_var_id` = `IN_VARIABLE_ID`. So, it ends up doing
nothing. E.g., adding `debug_assert_eq!(new_var_id, IN_VARIABLE_ID)` in
`replace_in_variable` does not trigger any panic.
# User-Facing Changes
Breaking change for `nu_protocol`.