`--list-undoc` breaks `yard doc` reporting

[ojab]

Steps to reproduce

class Xxx
  def x
    puts 'xxx'
  end
end

$ yard doc xxx.rb 
Files:           1
Modules:         0 (    0 undocumented)
Classes:         1 (    1 undocumented)
Constants:       0 (    0 undocumented)
Attributes:      0 (    0 undocumented)
Methods:         1 (    1 undocumented)
 0.00% documented
$ yard doc --list-undoc xxx.rb 
[warn]: Unrecognized/invalid option: --list-undoc
Files:           0
Modules:         0 (    0 undocumented)
Classes:         0 (    0 undocumented)
Constants:       0 (    0 undocumented)
Attributes:      0 (    0 undocumented)
Methods:         0 (    0 undocumented)
 100.00% documented
$ yard doc --list-undoc --db .yardoc/ xxx.rb 
[warn]: Unrecognized/invalid option: --list-undoc
Files:           1
Modules:         0 (    0 undocumented)
Classes:         1 (    1 undocumented)
Constants:       0 (    0 undocumented)
Attributes:      0 (    0 undocumented)
Methods:         1 (    1 undocumented)
 0.00% documented

Undocumented Objects:

(in file: xxx.rb)
Xxx
Xxx#x

I suppose db should be implicitly set and --list-undoc should be added to the list of supported options.

Environment details:

• OS: linux x86_64
• Ruby version (ruby -v): ruby 3.0.1p64 (2021-04-05 revision 0fb782ee38) [x86_64-linux]
• YARD version (yard -v): yard 0.9.26
• Relevant software dependency/versions:
  • [Any 3rd party libs required to reproduce, omit if none]

I have read the Contributing Guide.

[lsegal]

--list-undoc is not supported in yard doc. That option is part of yard stats.

The command above worked due to internal behavior, but it is considered undefined behavior to use yard doc --list-undoc