Resolve only an assigned source length unit, matching STEP writer eligibility.
Overlay-created projects/assignments/units cannot supply source STEP bytes;
projectIds must already contain only current effective IfcProject ids,
with deleted/retyped projects excluded (use iterateEffectiveEntities).
isDeleted filters assignment/unit references, not the project inventory.
Deleted references and unsupported names return null. #7355
Resolve only an assigned source length unit, matching STEP writer eligibility. Overlay-created projects/assignments/units cannot supply source STEP bytes;
projectIdsmust already contain only current effective IfcProject ids, with deleted/retyped projects excluded (use iterateEffectiveEntities).isDeletedfilters assignment/unit references, not the project inventory. Deleted references and unsupported names return null. #7355