The reason why this was done was partial loading, where we need to keep track of
afterSum, and that involves calculating the sum of all slices.
I've relaxed the restriction now - if the data isn't paritally loaded, invalid slices will be simply ignored and a warning will be issued instead of an error.
FacetChart doesn't have such a restriction because FacetChart can display negative values, it can display nonexistant values, it doesn't need to calculate the percentage of the total (even in partial loading), and each "slice" can have multiple values, so there is no requirement to have a property named "value". However if you add actual invalid values (like
"hello") to a FacetChart slice, you will still get an error.
This fix will be available in the next update, sometime this week.