Problem/Motivation

For citation styles which use label elements in groups, sometimes the conditional aspect of groups is not present. This is notable in the APA style. For a book publication which has no volume, the style's volume-booklike macro implicitly outputs the not-present number-of-volumes property, resulting in an output of 1–

Wildcat, W. (2024). History of Wildcats. In Wildcat Anthology (Version V1, 1–, Issues 4, pp. 200-230). The University of Arizona Press.

Describe the bug

Group rendering of seboettg/citeproc-php currently does not seem to take into account the conditional nature of a Group element which contains a Label. This is explained in seboettg/citeproc-php#158

To Reproduce

Create a book publication with no volume, while using the APA style.

Expected behavior

Wildcat, W. (2024). History of Wildcats. In Wildcat Anthology (Version V1, Issues 4, pp. 200-230). The University of Arizona Press.