public void setSectionIsCollapsed(int sectionIndex, boolean collapsed) {
        boolean notify = isSectionCollapsed(sectionIndex) != collapsed;

        collapsedSections.put(sectionIndex, collapsed);

        if (notify) {
            if (sections == null) {
                buildSectionIndex();
            }

            Section section = sections.get(sectionIndex);
            int number = section.numberOfItems;

            if (collapsed) {
                notifySectionItemRangeRemoved(sectionIndex, 0, number, false);
            } else {
                notifySectionItemRangeInserted(sectionIndex, 0, number, false);
            }
        }
    }
Mark that a section is collapsed or not. By default sections are not collapsed and draw
all their child items. By "collapsing" a section, the child items are hidden.

@param sectionIndex index of section
@param collapsed    if true, section is collapsed, false, it's open
android/modules/module_common/src/main/java/github/tornaco/android/thanos/widget/section/SectioningAdapter.java