`WEBrick::HTTPUtils.escape(nil)` raises a confusing exception

[kyoshidajp]

% irb
> RUBY_VERSION
=> "3.1.2"

> require 'webrick'
> WEBrick::HTTPUtils.escape(nil)
/Users/katsuhiko.yoshida/.rbenv/versions/3.1.2/lib/ruby/gems/3.1.0/gems/webrick-1.7.0/lib/webrick/httputils.rb:444:in `_escape': undefined method `b' for nil:NilClass (NoMethodError)

      str = str.b
               ^^

(omit)

%irb
> RUBY_VERSION
=> "2.7.6"

> WEBrick::HTTPUtils.escape(nil)
Traceback (most recent call last):
        7: from /Users/katsuhiko.yoshida/.rbenv/versions/2.7.6/bin/irb:23:in `<main>'
        6: from /Users/katsuhiko.yoshida/.rbenv/versions/2.7.6/bin/irb:23:in `load'
        5: from /Users/katsuhiko.yoshida/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/irb-1.2.6/exe/irb:11:in `<top (required)>'
        4: from (irb):2
        3: from (irb):3:in `rescue in irb_binding'
        2: from /Users/katsuhiko.yoshida/.rbenv/versions/2.7.6/lib/ruby/2.7.0/webrick/httputils.rb:467:in `escape'
        1: from /Users/katsuhiko.yoshida/.rbenv/versions/2.7.6/lib/ruby/2.7.0/webrick/httputils.rb:443:in `_escape'
NoMethodError (undefined method `b' for nil:NilClass)

WEBrick::HTTPUtils.escape_form(nil) is also the same. If the exception was raised in complex situations (e.g. in third party library), it will be difficult to determine the cause (parameter is nil).

My suggestions are following.

1. Raises a builtin exception
   • CGI.escape is this behavior (raises a TypeError)
2. Raises a custom exception
   • Like a EscapeError
3. Returns ""
   • URI.encode_www_form_component and ERB::Util.url_encode are this behavior
   • But, BREAKING CHANGE (doesn't stop)

Thank you for your great work.

[tisba]

Indeed this is confusing and not nice to handle for 3rd party code.

re 1) AFAIK CGI.escape raising a TypeError (with no implicit conversion of nil into String) is not necessarily meant as input validation check, it just fails as part of its internal workings.

re 3) While just retuning nil or "" could be something for a new API, I think that might be a bad idea for WEBrick today.

I personally would suggest raising an ArgumentError in this case.