Thre are real world `REXML::Document.new("")` usages

[kou]

First of all, thanks for the work on this project. 🙇

I'm noticing this handles empty string but not nil input.

In 3.4.2, they had the same behavior:

irb(main):003> REXML::Document.new("")
=> <UNDEFINED/>
irb(main):004> REXML::Document.new(nil)
=> <UNDEFINED/>

Now, in 3.4.3, the behavior is changed:

irb(main):002> REXML::Document.new("")
../.gem/ruby/3.3.9/gems/rexml-3.4.3/lib/rexml/parsers/baseparser.rb:271:in `pull_event': Malformed XML: No root element (REXML::ParseException)
Line: 0
Position: 0
Last 80 unconsumed characters:

	from ../.gem/ruby/3.3.9/gems/rexml-3.4.3/lib/rexml/parsers/baseparser.rb:249:in `pull'
	from ../.gem/ruby/3.3.9/gems/rexml-3.4.3/lib/rexml/parsers/treeparser.rb:21:in `parse'
	from ../.gem/ruby/3.3.9/gems/rexml-3.4.3/lib/rexml/document.rb:466:in `build'
	from ../.gem/ruby/3.3.9/gems/rexml-3.4.3/lib/rexml/document.rb:103:in `initialize'
	from (irb):2:in `new'
	from (irb):2:in `<main>'
	from <internal:kernel>:187:in `loop'
	from ../.gem/ruby/3.3.9/gems/bundler-2.6.2/lib/bundler/cli/console.rb:16:in `run'
	from ../.gem/ruby/3.3.9/gems/bundler-2.6.2/lib/bundler/cli.rb:482:in `console'
	from ../.gem/ruby/3.3.9/gems/bundler-2.6.2/lib/bundler/vendor/thor/lib/thor/command.rb:28:in `run'
	from ../.gem/ruby/3.3.9/gems/bundler-2.6.2/lib/bundler/vendor/thor/lib/thor/invocation.rb:127:in `invoke_command'
	from ../.gem/ruby/3.3.9/gems/bundler-2.6.2/lib/bundler/vendor/thor/lib/thor.rb:538:in `dispatch'
	from ../.gem/ruby/3.3.9/gems/bundler-2.6.2/lib/bundler/cli.rb:35:in `dispatch'
	from ../.gem/ruby/3.3.9/gems/bundler-2.6.2/lib/bundler/vendor/thor/lib/thor/base.rb:584:in `start'
	from ../.gem/ruby/3.3.9/gems/bundler-2.6.2/lib/bundler/cli.rb:29:in `start'
	from ../.gem/ruby/3.3.9/gems/bundler-2.6.2/exe/bundle:28:in `block in <top (required)>'
	... 4 levels...
irb(main):003> REXML::Document.new(nil)
=> <UNDEFINED/>

Finally, should this print a warning in a patch release (3.4.x) and raise in the next minor release (3.5.x)? I noticed this because rexml hasn't validated this forever so there's possibly other code that was creating a document and adding elements later, see: https://github.com/search?q=REXML%3A%3ADocument.new%28%22%22%29&type=code

Thanks!

Originally posted by @jrafanie in #291 (comment)

[kou]

Thanks for sharing the information.

How about treating REXML::Document.new("") as REXML::Document.new(nil) for keeping backward compatibility?
(Note that REXML::Document.new(" ") (not an empty input) still rejects the input.)

Copied from #291 (comment)

[kou]

See also other comments in #291.

[jrafanie]

Thank you for opening the issue and resolving it @kou ❤️

[kou]

@naitoh implemented it. :-)