message: improve not rich tooltip
diff: @@ -1230,7 +1230,9 @@ class NVD3TimeSeriesViz(NVD3Viz):
  comparison_type = fd.get('comparison_type') or 'values'
  df = self.process_data(df)
  if comparison_type == 'values':
  - chart_data = self.to_series(df)
  + # Filter out series with all NaN
  + chart_data = self.to_series(df.dropna(axis=1, how='all'))
  +
  for i, (label, df2) in enumerate(self._extra_chart_data):
  chart_data.extend(
  self.to_series(
  