Style/OperatorMethodCall cop causes an error with the expression like obj.!

[092tsaito]

An error occurred while Style/OperatorMethodCall cop was inspecting a file
which contains the expression like obj.!

---

Steps to reproduce the problem

1. Create a Ruby file foo.rb

class Foo
  def sample(arg)
    arg.!
  end
end

2. run rubocop --debug foo.rb

# bundle exec rubocop --debug foo.rb
For /app/app/models: configuration from /app/.rubocop.yml
configuration from /app/vendor/bundle/ruby/2.7.0/gems/rubocop-rails-2.16.1/config/default.yml
configuration from /app/vendor/bundle/ruby/2.7.0/gems/rubocop-rails-2.16.1/config/default.yml
Default configuration from /app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/config/default.yml
configuration from /app/vendor/bundle/ruby/2.7.0/gems/rubocop-rspec-2.13.2/config/default.yml
configuration from /app/vendor/bundle/ruby/2.7.0/gems/rubocop-rspec-2.13.2/config/default.yml
Inheriting configuration from /app/.rubocop_todo.yml
Use parallel by default.
Skipping parallel inspection: only a single file needs inspection
Inspecting 1 file
Scanning /app/app/models/foo.rb
An error occurred while Style/OperatorMethodCall cop was inspecting /app/app/models/foo.rb:3:4.
undefined method `children' for nil:NilClass
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cop/style/operator_method_call.rb:30:in `on_send'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cop/commissioner.rb:136:in `public_send'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cop/commissioner.rb:136:in `block (2 levels) in trigger_restricted_cops'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cop/commissioner.rb:160:in `with_cop_error_handling'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cop/commissioner.rb:135:in `block in trigger_restricted_cops'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cop/commissioner.rb:134:in `each'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cop/commissioner.rb:134:in `trigger_restricted_cops'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cop/commissioner.rb:70:in `on_send'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-ast-1.23.0/lib/rubocop/ast/traversal.rb:153:in `on_def'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cop/commissioner.rb:71:in `on_def'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-ast-1.23.0/lib/rubocop/ast/traversal.rb:153:in `on_class'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cop/commissioner.rb:71:in `on_class'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-ast-1.23.0/lib/rubocop/ast/traversal.rb:20:in `walk'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cop/commissioner.rb:86:in `investigate'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cop/team.rb:155:in `investigate_partial'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cop/team.rb:83:in `investigate'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/runner.rb:315:in `inspect_file'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/runner.rb:259:in `block in do_inspection_loop'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/runner.rb:293:in `block in iterate_until_no_changes'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/runner.rb:286:in `loop'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/runner.rb:286:in `iterate_until_no_changes'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/runner.rb:255:in `do_inspection_loop'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/runner.rb:138:in `block in file_offenses'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/runner.rb:163:in `file_offense_cache'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/runner.rb:137:in `file_offenses'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/runner.rb:128:in `process_file'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/runner.rb:109:in `block in each_inspected_file'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/runner.rb:108:in `each'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/runner.rb:108:in `reduce'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/runner.rb:108:in `each_inspected_file'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/runner.rb:94:in `inspect_files'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/runner.rb:47:in `run'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cli/command/execute_runner.rb:26:in `block in execute_runner'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cli/command/execute_runner.rb:52:in `with_redirect'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cli/command/execute_runner.rb:25:in `execute_runner'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cli/command/execute_runner.rb:17:in `run'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cli/command.rb:11:in `run'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cli/environment.rb:18:in `run'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cli.rb:72:in `run_command'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cli.rb:79:in `execute_runners'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/lib/rubocop/cli.rb:48:in `run'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/exe/rubocop:19:in `block in <top (required)>'
/app/vendor/bundle/ruby/2.7.0/gems/benchmark-0.2.0/lib/benchmark.rb:311:in `realtime'
/app/vendor/bundle/ruby/2.7.0/gems/rubocop-1.37.0/exe/rubocop:19:in `<top (required)>'
/app/vendor/bundle/ruby/2.7.0/bin/rubocop:25:in `load'
/app/vendor/bundle/ruby/2.7.0/bin/rubocop:25:in `<top (required)>'
/root/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/bundler-2.3.4/lib/bundler/cli/exec.rb:58:in `load'
/root/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/bundler-2.3.4/lib/bundler/cli/exec.rb:58:in `kernel_load'
/root/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/bundler-2.3.4/lib/bundler/cli/exec.rb:23:in `run'
/root/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/bundler-2.3.4/lib/bundler/cli.rb:484:in `exec'
/root/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/bundler-2.3.4/lib/bundler/vendor/thor/lib/thor/command.rb:27:in `run'
/root/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/bundler-2.3.4/lib/bundler/vendor/thor/lib/thor/invocation.rb:127:in `invoke_command'
/root/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/bundler-2.3.4/lib/bundler/vendor/thor/lib/thor.rb:392:in `dispatch'
/root/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/bundler-2.3.4/lib/bundler/cli.rb:31:in `dispatch'
/root/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/bundler-2.3.4/lib/bundler/vendor/thor/lib/thor/base.rb:485:in `start'
/root/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/bundler-2.3.4/lib/bundler/cli.rb:25:in `start'
/root/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/bundler-2.3.4/exe/bundle:48:in `block in <top (required)>'
/root/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/bundler-2.3.4/lib/bundler/friendly_errors.rb:103:in `with_friendly_errors'
/root/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/bundler-2.3.4/exe/bundle:36:in `<top (required)>'
/root/.rbenv/versions/2.7.6/bin/bundle:25:in `load'
/root/.rbenv/versions/2.7.6/bin/bundle:25:in `<main>'
.

1 file inspected, no offenses detected

1 error occurred:
An error occurred while Style/OperatorMethodCall cop was inspecting /app/app/models/foo.rb:3:4.
Errors are usually caused by RuboCop bugs.
Please, report your problems to RuboCop's issue tracker.
https://github.com/rubocop/rubocop/issues

Mention the following information in the issue report:
1.37.0 (using Parser 3.1.2.1, rubocop-ast 1.23.0, running on ruby 2.7.6) [x86_64-linux]
Finished in 0.4347307999996701 seconds

RuboCop version

$ [bundle exec] rubocop -V
1.37.0 (using Parser 3.1.2.1, rubocop-ast 1.23.0, running on ruby 2.7.6) [x86_64-linux]
  - rubocop-rails 2.16.1
  - rubocop-rspec 2.13.2