def _get_hover_data(self, data, element, empty=False):
        if 'hover' in self.default_tools + self.tools:
            for d in element.dimensions(label=True):
                sanitized = util.dimension_sanitizer(d)
                data[sanitized] = [] if empty else element.dimension_values(d)
:returns: JSONized default Cluster attributes.
dataset/ETHPy150Open ioam/holoviews/holoviews/plotting/bokeh/element.py/ElementPlot._get_hover_data--crossover with--dataset/ETHPy150Open openstack/fuel-web/nailgun/nailgun/api/v1/handlers/cluster.py/ClusterAttributesDefaultsHandler.GET