Cannot put 2 ActiveRecords of different classes in the same array

[softwaregravy]

Putting 2 objects of different active record classes into the same array causes an exception:

irb(main):001:0> c1 = MyFirstClass.first
irb(main):002:0> c2 = MySecondClass.first
irb(main):003:0> [c1, c2]
    .../ruby-2.4.4@XXX/gems/activemodel-5.2.0/lib/active_model/attribute_methods.rb:430:in `method_missing'
    .../ruby-2.4.4@XXX/gems/hirb-0.7.3/lib/hirb/helpers/object_table.rb:10:in `block (2 levels) in render'
    .../ruby-2.4.4@XXX/gems/hirb-0.7.3/lib/hirb/helpers/object_table.rb:10:in `each'
    .../ruby-2.4.4@XXX/gems/hirb-0.7.3/lib/hirb/helpers/object_table.rb:10:in `inject'
    .../ruby-2.4.4@XXX/gems/hirb-0.7.3/lib/hirb/helpers/object_table.rb:10:in `block in render'
    .../ruby-2.4.4@XXX/gems/hirb-0.7.3/lib/hirb/helpers/object_table.rb:9:in `each'
    .../ruby-2.4.4@XXX/gems/hirb-0.7.3/lib/hirb/helpers/object_table.rb:9:in `inject'
    .../ruby-2.4.4@XXX/gems/hirb-0.7.3/lib/hirb/helpers/object_table.rb:9:in `render'
    .../ruby-2.4.4@XXX/gems/hirb-0.7.3/lib/hirb/helpers/auto_table.rb:22:in `render'
    .../ruby-2.4.4@XXX/gems/hirb-0.7.3/lib/hirb/formatter.rb:73:in `_format_output'
    .../ruby-2.4.4@XXX/gems/hirb-0.7.3/lib/hirb/formatter.rb:56:in `format_output'
    .../ruby-2.4.4@XXX/gems/hirb-0.7.3/lib/hirb/view.rb:205:in `render_output'
    .../ruby-2.4.4@XXX/gems/hirb-0.7.3/lib/hirb/view.rb:123:in `view_output'
    .../ruby-2.4.4@XXX/gems/hirb-0.7.3/lib/hirb/view.rb:201:in `view_or_page_output'
    .../ruby-2.4.4@XXX/gems/hirb-0.7.3/lib/hirb/view.rb:187:in `output_value'
    .../ruby-2.4.4@XXX/rubies/ruby-2.4.4/lib/ruby/2.4.0/irb.rb:494:in `block (2 levels) in eval_input'   
...

rails 5.2.0 ruby 2.4.4 hirb 0.7.3