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

从 lib/webrick/httputils.rb 中 HTTPUtils.escape 和 _escape 附近开始，然后将报告的 nil 行为与 escape_form(nil) 进行比较。对照 CGI.escape、URI.encode_www_form_component 和 ERB::Util.url_encode 检查提出的三种结果；完成此项工作需要 maintainer 决定预期的 nil 行为，并提供相应的覆盖率。

% 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.