How to use the fitlins.interfaces.utils.CollateWithMetadata function in fitlins

def __init__(self, fields=None, **kwargs):
        super(CollateWithMetadata, self).__init__(**kwargs)
        if not fields:
            fields = self.inputs.field_to_metadata_map.keys()
            if not fields:
                raise ValueError("Fields must be a non-empty list")

        self._fields = fields
        add_traits(self.inputs, fields)

#
        # Plotting
        #

        plot_contrasts = pe.MapNode(
            GlassBrainPlot(image_type='png'),
            iterfield='data',
            name='plot_{}_contrasts'.format(level))

        #
        # Derivatives
        #

        collate_outputs = pe.Node(
            CollateWithMetadata(
                fields=['effect_maps', 'variance_maps', 'stat_maps', 'pvalue_maps', 'zscore_maps'],
                field_to_metadata_map={
                    'effect_maps': {'stat': 'effect'},
                    'variance_maps': {'stat': 'variance'},
                    'pvalue_maps': {'stat': 'p'},
                    'zscore_maps': {'stat': 'z'},
                }),
            name=f'collate_{level}_outputs')

        ds_contrast_maps = pe.Node(
            BIDSDataSink(base_directory=out_dir,
                         path_patterns=contrast_pattern),
            run_without_submitting=True,
            name='ds_{}_contrast_maps'.format(level))

        ds_contrast_plots = pe.Node(