Style/ArgumentsForwarding with added arguments on Ruby 3.1 results in an error

[herwinw]

With the Ruby 3.1 config:

AllCops:
  NewCops: enable
  TargetRubyVersion: 3.1

The following code results in a runtime error:

def foo(**kwargs, &)
  bar(1, **kwargs, &)
end

An error occurred while Style/ArgumentsForwarding cop was inspecting poc.rb:1:0.
undefined method `+' for nil:NilClass

            arg_after_splat = arguments[splat_index + 1]
                                                    ^
vendor/bundle/ruby/3.1.0/gems/rubocop-1.56.0/lib/rubocop/cop/style/arguments_forwarding.rb:336:in `no_post_splat_args?'
[.. more backtrace ...]

RuboCop version

This is a regression in 1.56.0, the same code does not result in crashes in 1.55.1

$ bundle exec rubocop -V
1.56.0 (using Parser 3.2.2.3, rubocop-ast 1.29.0, running on ruby 3.1.2) [x86_64-linux-gnu]