How can Bokeh DataCube widget's SumAggregator to sum more than 1 field

Question

How can Bokeh 1.3 new widget DataCube to sum more than 1 field?

Bokeh 1.3 doc :https://blog.bokeh.org/posts/release-1-3-0

From the sample code of Bokeh doc, it will sum 1 field only, I have tried with a list of 2 fields but no luck.

Sample codes:

source = ColumnDataSource(data=dict(
    d0=['A', 'E', 'E', 'E', 'J', 'L', 'M'],
    d1=['B', 'D', 'D', 'H', 'K', 'L', 'N'],
    d2=['C', 'F', 'G', 'H', 'K', 'L', 'O'],
    px=[10,  20,  30,  40,  50,  60,  70 ],
))

target = ColumnDataSource(data=dict(row_indices=[], labels=[]))

formatter = StringFormatter(font_style='bold')

columns = [
    TableColumn(field='d2', title='Name', width=40, sortable=False, formatter=formatter),
    TableColumn(field='px', title='Price', width=40, sortable=False),
]

grouping = [
    GroupingInfo(getter='d0', aggregators=[SumAggregator(field_='px')]),
    GroupingInfo(getter='d1', aggregators=[SumAggregator(field_='px')])
]

cube = DataCube(source=source, columns=columns, grouping=grouping, target=target)

Any help is great, thanks.