@staticmethod
def _diff_plus_minus(is_added):
    if (is_added is None):
        return ''
    if is_added:
        return '<font color="forestgreen">+</font>'
    return '<font color="red">-</font>'
@staticmethod
def _diff_plus_minus(is_added):
    if (is_added is None):
        return 
    if is_added:
        return '<font color="forestgreen">+</font>'
    return '<font color="red">-</font>'