Inconsistency in missing parent exception between readonly and mut

[eleftherioszisis]

import morphio
m = morphio.Morphology(filename).root_sections[0].parent

raises:

MissingParentError: Cannot call Section::parent() on a root node (section id=0).

while:

import morphio
m = morphio.mut.Morphology(filename).root_sections[0].parent

raises:

IndexError: map::at

It is important for readonly and mut to exhibit similar behaviour so that they can be used by algorithms interchangeably.

[asanin-epfl]

Tom, please look if you have a moment.

[tomdele]

Yeah I will try to check that

[tomdele]

Elef you are the king of this ticket now congratz ! :D