>If index argument is NULL, why bother setting this internal variable _index?
This assignment is intended to support `index` as an optional output parameter: callers can pass NULL if they only care about the return value. This approach avoids repeated `if
(index)` checks by aliasing to a local dummy variable upfront.
Would you be happy for me to retain this pattern, renaming the dummy variable to make it clearer, e.g.:
```
uint8_t dummy_index;
index = index ? index : &dummy_index;
```
I would also update the documentation to clarify that index is optional.
Alternatively, if you’d prefer to disallow NULL for index and require the caller to always provide a valid pointer, I’m happy to change it accordingly.
Many thanks,
Hari
