'Makes first \'H\' in str representation non-optional.
str(timedelta) has [H]H:MM:SS format, which is not suitable
for front-end (and ISO time standard), so we force HH:MM:SS format.'

def timedelta_to_string(self, value):

    stringified = str(value)
    if (len(stringified) == 7):
        stringified = ('0' + stringified)
    return stringified
