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: explain_pretty_printer.rb
    path of file: ./repos/stackneveroverflow/vendor/bundle/ruby/2.3.0/gems/activerecord-5.0.3/lib/active_record/connection_adapters/mysql
    
    the code of the file until where you have to start completion: module ActiveRecord
  module ConnectionAdapters
    module MySQL
      class ExplainPrettyPrinter # :nodo
    
        def build_cells(items, widths)
          cells = []
          items.each_with_index do |item, i|
            item = 'NULL' if item.nil?
            justifier = item.is_a?(Numeric) ? 'rjust' : 'ljust'
            cells << item.to_s.send(justifier, widths[i])
          end
          '| ' + cells.join(' | ') + ' |'
        end