Get the label of the Dataset.

        Returns
        -------
        label : numpy array or None
            The label information from the Dataset.

def get_label(self):
        """Get the label of the Dataset.

        Returns
        -------
        label : numpy array or None
            The label information from the Dataset.
        """
        if self.label is None:
            self.label = self.get_field('label')
        return self.label