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: node_spec.rb
    path of file: ./repos/mutant/spec/unit/mutant/mutator
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

aggregate = Hash.new { |hash, key| ha
    
        def dispatch
          left
          emit_left(s(:int, 1))
          emit_left_mutations
          emit_right_mutations do |node|
            node.eql?(s(:nil))
          end
        end