Issues #31 #38:  does the cell contain a blank line? In that case
    we add an end-of-cell marker

def endofcell_marker(source, comment):
    """Issues #31 #38:  does the cell contain a blank line? In that case
    we add an end-of-cell marker"""
    endofcell = '-'
    while True:
        endofcell_re = re.compile(r'^{}( )'.format(comment) + endofcell + r'\s*$')
        if list(filter(endofcell_re.match, source)):
            endofcell = endofcell + '-'
        else:
            return endofcell