Programming Ruby 3.2 (5th Edition): B2.0 page 306, String or String?

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@noelrappin

page 306 : When I run % typeprof gems/aaagmnr/lib/aaagmnr.rb, I have a small difference : String? instead of String for attr_reader dictionary:.

% diff gems/types_book.txt gems/types_my.txt
17c17
<     attr_reader dictionary: String
---
>     attr_reader dictionary: String?
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That’s what I get now, too. I wonder if typeprof changed slightly at some point.