`Expected start tag <core:externalreference>` inside a <core:externalReference>

[Fordi]

When libcitygml encounters the following structure, it throws Expected start tag <core:externalreference>, but got <core:informationsystem>:

      <core:externalReference>
        <core:informationSystem>http://repository.gdi-de.org/schemas/adv/citygml/fdv/art.htm#_9100</core:informationSystem>
        <core:externalObject>
          <core:name>DESNATPU1000HPBi</core:name>
        </core:externalObject>
      </core:externalReference>

This was found attempting to parse the following data file from the official German open data for the state of the Saxany:

lod2_33460_5668_2_sn_citygml.zip

[javagl]

How up to date is the TODO list at https://github.com/jklimke/libcitygml/blob/master/TODO.md ? It contains the point

Implement parsing of CityObject <externalReference> member

It does appear in the code many times, so from skimming over it, it's not clear whether this may alread have been addressed.

(What's a "tiny red flag" for my nerd brain is tha the error message says externalreference, and the tag name is externalReference - could captitalization play a role here, anywhere...?)