A special annotation intended solely for representing the bottom type in
the qualifier hierarchy.
This qualifier is only used automatically if the existing qualifiers do not have a
bottom type.
Other type systems could reuse this qualifier instead of introducing their own
dedicated bottom qualifier. The programmer would then use methods like
TreeAnnotator.addTreeKind(com.sun.source.tree.Tree.Kind, javax.lang.model.element.AnnotationMirror) to
add implicit annotations and needs to manually add the bottom qualifier to the
qualifier hierarchy.
Programmers cannot write this qualifier in source code.