getLinkAttribute<R>  method 
Get attribute of given generic type R for a link series
Implementation
R? getLinkAttribute<R>(AttributeKey<R> key) {
  return linkAttributes.getAttr<R>(key);
}Get attribute of given generic type R for a link series
R? getLinkAttribute<R>(AttributeKey<R> key) {
  return linkAttributes.getAttr<R>(key);
}