    # File lib/chef/resource/conditional.rb, line 45
          def initialize(positivity, command=nil, command_opts={}, &block)
            @positivity = positivity
            case command
            when String
              @command, @command_opts = command, command_opts
              @block = nil
            when nil
              raise ArgumentError, "only_if/not_if requires either a command or a block" unless block_given?
              @command, @command_opts = nil, nil
              @block = block
            else
              raise ArgumentError, "Invalid only_if/not_if command: #{command.inspect} (#{command.class})"
            end
          end