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

[YOSHIDA Katsuhiko]

% 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.