You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: association_tree.rb
    path of file: ./repos/activegraph/lib/active_graph/node/query/query_proxy_eager_loading
    
    the code of the file until where you have to start completion: module ActiveGraph
  module Node
    module Query
      module QueryProxyEagerLoading
        class AssociationTree < Hash
          attr_accessor :model, 
    
          def add_spec(spec)
            fail_spec(spec) unless model

            case spec
            when nil
              nil
            when Array
              spec.each(&method(:add_spec))
            when Hash
              process_hash(spec)
            when String
              process_string(spec)
            else
              add_key(spec)
            end