public int getSectionIndex(final Section section) {
        int index = 0;

        for (final Map.Entry<String, Section> entry : this.sections.entrySet()) {
            if (entry.getValue() == section) {
                return index;
            }
            index++;
        }

        return -1;
    }
Returns the index of the first occurrence of the specified section in this adapter, or -1 if
this adapter does not contain the section. Note that, the visibility of section is being
ignored.

@param section section to search for
@return the index of the first occurrence of the specified section in this adapter, or -1 if
this adapter does not contain the section
library/src/main/java/io/github/luizgrp/sectionedrecyclerviewadapter/SectionedRecyclerViewAdapter.java