message: fixing chart keys in MultiLineViz
diff: @@ -1463,10 +1463,14 @@ class MultiLineViz(NVD3Viz):
  x_values = [value["x"] for value in series["values"]]
  min_x = min(x_values + ([min_x] if min_x is not None else []))
  max_x = max(x_values + ([max_x] if max_x is not None else []))
  -
  + series_key = (
  + series["key"]
  + if isinstance(series["key"], (list, tuple))
  + else [series["key"]]
  + )
  data.append(
  {
  - "key": prefix + ", ".join(series["key"]),
  + "key": prefix + ", ".join(series_key),
  "type": "line",
  "values": series["values"],
  "yAxis": y_axis,
  