public void notifySectionRemoved(int sectionIndex) {
        if (sections == null) {
            buildSectionIndex();
            notifyAllSectionsDataSetChanged();
        } else {
            Section section = this.sections.get(sectionIndex);
            buildSectionIndex();
            notifyItemRangeRemoved(section.adapterPosition, section.length);
        }

        updateCollapseAndSelectionStateForSectionChange(sectionIndex, -1);
    }
Notify that a section has been removed

@param sectionIndex position of the removed section
android/modules/module_common/src/main/java/github/tornaco/android/thanos/widget/section/SectioningAdapter.java