public void notifySectionFooterInserted(int sectionIndex) {
        if (sections == null) {
            buildSectionIndex();
            notifyAllSectionsDataSetChanged();
        } else {
            buildSectionIndex();
            Section section = this.sections.get(sectionIndex);
            if (!section.hasFooter) {
                throw new IllegalArgumentException("notifySectionFooterInserted: adapter implementation reports that section " + sectionIndex + " does not have a footer");
            }
            notifyItemInserted(section.adapterPosition + section.length - 1);
        }
    }
Notify that a section has had a footer added to it

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