You can set a threshold for a pie chart which will group slices that are in value less than the threshold.
Here is the code on how to do this:
nav: {
"threshold":"5%",
"others": {
"text":"Others",
"backgroundColor":"black"
}
}
The others object sets the slice that includes all slices that are under the threshold level.
Here is a demo that shows how threshold works for pie charts: Demo