@staticmethod
def set_absolute_end_of_labels(label_list):
    """
        If there are any labels where the end is defined as -1 (end of utterance),
        set the concrete time.

        Arguments:
            label_list (LabelList): The label-list to process.
        """
    for label in sorted(label_list, key=lambda x: x.start):
        if label.end <= label.start:
            raise ValueError('Label-end {} is smaller than label-start {}!'
                .format(label.end, label.start))
        if label.value is not '###############':
            if label.end == -1:
                label.end = label.label_list.utterance.end
            if label.end == -1:
                label.end = (label.label_list.utterance.file.duration -
                    label.label_list.utterance.start)
    return label_list
