feat: improve real-time chart example; add small refinements to via core files

h/util.go

@@ -7,6 +7,10 @@ import (
 func retype(nodes []H) []g.Node {
 	list := make([]g.Node, len(nodes))
 	for i, node := range nodes {
+		if node == nil {
+			list[i] = nil
+			continue
+		}
 		list[i] = node.(g.Node)
 	}
 	return list