the label for a group whose key is null/undefined/empty — prevents a band
from literally showing "null"/"undefined" (real DB data can always have NULL mixed into a
group column); overridable via headerLabel/footerLabel, which receive this key to transform
further — English (2026-07-07 — was Thai '(ไม่ระบุ)') for the same zero-config reason as
DEFAULT_SUMMARY_LABEL: a group with no font registered shouldn't hit the Thai font guard
just from an unspecified key
the label for a group whose key is null/undefined/empty — prevents a band from literally showing "null"/"undefined" (real DB data can always have NULL mixed into a group column); overridable via headerLabel/footerLabel, which receive this key to transform further — English (2026-07-07 — was Thai '(ไม่ระบุ)') for the same zero-config reason as DEFAULT_SUMMARY_LABEL: a group with no font registered shouldn't hit the Thai font guard just from an unspecified key