Methods not implemented? centroid_distances, centroid_distance

[alxx]

I was looking at the public methods available on a centroid instance and I found these two. The first one is nil, the other one causes an error:

3.4.7 :067 > kmeans.clusters[0].centroid.methods - 1.methods
 => [:label=, :centroid_distances, :dimension, :centroid_distance, :data, :cluster, :cluster=, :label, :to_a, :id] 

3.4.7 :070 > kmeans.clusters[0].centroid.centroid_distances
 => nil 

3.4.7 :071 > kmeans.clusters[0].centroid.centroid_distance
/home/alxx/.rvm/gems/ruby-3.4.7/gems/kmeans-clusterer-0.11.4/lib/kmeans-clusterer.rb:92:in 'KMeansClusterer::Point#centroid_distance': undefined method 'id' for nil (NoMethodError)

      @centroid_distances[@cluster.id]
                                  ^^^
	from (irb):71:in '<main>'
	from <internal:kernel>:168:in 'Kernel#loop'
	from /home/alxx/.rvm/gems/ruby-3.4.7/gems/irb-1.15.2/exe/irb:9:in '<top (required)>'
	from /home/alxx/.rvm/gems/ruby-3.4.7/bin/irb:25:in 'Kernel#load'
	from /home/alxx/.rvm/gems/ruby-3.4.7/bin/irb:25:in '<main>'
	from /home/alxx/.rvm/gems/ruby-3.4.7/bin/ruby_executable_hooks:22:in 'Kernel#eval'
	from /home/alxx/.rvm/gems/ruby-3.4.7/bin/ruby_executable_hooks:22:in '<main>'

Or am I using them wrong?