# File lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph.rb, line 91
    def add_child_vertex(name, payload, parent_names, requirement)
      is_root = parent_names.include?(nil)
      parent_nodes = parent_names.compact.map { |n| vertex_named(n) }
      vertex = vertex_named(name) || if is_root
                                       add_root_vertex(name, payload)
                                     else
                                       add_vertex(name, payload)
                                     end
      vertex.payload ||= payload
      parent_nodes.each do |parent_node|
        add_edge(parent_node, vertex, requirement)
      end
      vertex
    end