this release implements the ability to set custom legend value(s) when the plot is un-hovered (#644).
as a consequence, it will now call any user-supplied series.value or series.values legend callbacks with value=null and dataIdx=null whenever the mouse cursor leaves the plotting area. previously, uPlot did not invoke these callbacks during mouseleave and simply put -- into the legend values.
therefore, if you neglected to handle null values in these user-supplied callbacks, your code may need to be updated.