Fix error when inspect is called but not found in inspector

[pocke]

Problem

When an object that doesn't have inspect method is displayed, it raises an error.

irb(main):001:0> BasicObject.new
(Object doesn't support #inspect)
Traceback (most recent call last):
       16: from /home/pocke/.rbenv/versions/trunk/bin/irb:23:in `load'
       15: from /home/pocke/.rbenv/versions/trunk/lib/ruby/gems/2.8.0/gems/irb-1.2.4/exe/irb:11:in `<top (required)>'
       14: from /home/pocke/.rbenv/versions/trunk/lib/ruby/2.8.0/irb.rb:399:in `start'
       13: from /home/pocke/.rbenv/versions/trunk/lib/ruby/2.8.0/irb.rb:470:in `run'
       12: from /home/pocke/.rbenv/versions/trunk/lib/ruby/2.8.0/irb.rb:470:in `catch'
       11: from /home/pocke/.rbenv/versions/trunk/lib/ruby/2.8.0/irb.rb:471:in `block in run'
       10: from /home/pocke/.rbenv/versions/trunk/lib/ruby/2.8.0/irb.rb:536:in `eval_input'
        9: from /home/pocke/.rbenv/versions/trunk/lib/ruby/2.8.0/irb/ruby-lex.rb:135:in `each_top_level_statement'
        8: from /home/pocke/.rbenv/versions/trunk/lib/ruby/2.8.0/irb/ruby-lex.rb:135:in `catch'
        7: from /home/pocke/.rbenv/versions/trunk/lib/ruby/2.8.0/irb/ruby-lex.rb:136:in `block in each_top_level_statement'
        6: from /home/pocke/.rbenv/versions/trunk/lib/ruby/2.8.0/irb/ruby-lex.rb:136:in `loop'
        5: from /home/pocke/.rbenv/versions/trunk/lib/ruby/2.8.0/irb/ruby-lex.rb:151:in `block (2 levels) in each_top_level_statement'
        4: from /home/pocke/.rbenv/versions/trunk/lib/ruby/2.8.0/irb.rb:537:in `block in eval_input'
        3: from /home/pocke/.rbenv/versions/trunk/lib/ruby/2.8.0/irb.rb:695:in `signal_status'
        2: from /home/pocke/.rbenv/versions/trunk/lib/ruby/2.8.0/irb.rb:541:in `block (2 levels) in eval_input'
        1: from /home/pocke/.rbenv/versions/trunk/lib/ruby/2.8.0/irb.rb:742:in `output_value'
NoMethodError (undefined method `include?' for nil:NilClass)
Maybe IRB bug!

Solution

Make sure the inspector returns a string.

It will display the following output.

irb(main):001:0> BasicObject.new
(Object doesn't support #inspect)
=> 

---

Note that it is the same with the previous behavior.

irb(main):001:0> RUBY_VERSION
=> "2.6.0"
irb(main):002:0> IRB::VERSION
=> "1.0.0"
irb(main):003:0> BasicObject.new
(Object doesn't support #inspect)
=>