Fix an error for Lint/ErbNewArguments cop

[koic]

This PR fixes the following error for Lint/ErbNewArguments cop when inspecting ActionView::Template::Handlers::ERB.new.

% cd path/to/rails/rails # rails/rails@f265e0dd
% bundle exec rubocop -d --only Lint/ErbNewArguments
actionview/lib/action_view/template/handlers.rb
For /Users/koic/src/github.com/rails/rails: configuration from
/Users/koic/src/github.com/rubocop-hq/rubocop/config/default.yml
Inspecting 1 file
Scanning
/Users/koic/src/github.com/rails/rails/actionview/lib/action_view/template/handlers.rb
An error occurred while Lint/ErbNewArguments cop was inspecting
/Users/koic/src/github.com/rails/rails/actionview/lib/action_view/template/handlers.rb:14:45.
undefined method `each_with_index' for nil:NilClass
/Users/koic/src/github.com/rubocop-hq/rubocop/lib/rubocop/cop/lint/erb_new_arguments.rb:89:in
`block in on_send'
/Users/koic/src/github.com/rubocop-hq/rubocop/lib/rubocop/cop/lint/erb_new_arguments.rb:90:in
`erb_new_with_non_keyword_arguments'
/Users/koic/src/github.com/rubocop-hq/rubocop/lib/rubocop/cop/lint/erb_new_arguments.rb:86:in
`on_send'

ActionView::Template::Handlers::ERB accepts new method without arguments, unlike standard ERB.

Below is the code that caused the error.

base.register_template_handler :erb, ERB.new

https://github.com/rails/rails/blob/v6.0.2.2/actionview/lib/action_view/template/handlers.rb#L16

It is an error if the standard ERB.new without arguments is used.
Therefore standard ERB.new and ActionView::Template::Handlers::ERB.new do not conflict.

% ruby -rerb -ve 'ERB.new'
ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [x86_64-darwin17]
Traceback (most recent call last):
        2: from -e:1:in `<main>'
        1: from -e:1:in `new'
/Users/koic/.rbenv/versions/2.7.0/lib/ruby/2.7.0/erb.rb:809:in
`initialize': wrong number of arguments (given 0, expected 1..4) (ArgumentError)

So including this patch in the cop will not interfere with linting to standard ERB.

---

Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[bbatsov]

Thanks!