Error in Style/RedundantParentheses

[lordofthelake]

Expected behavior

Rubocop should just lint the file and not throw an error.

Actual behavior

An error occurs in the Style/RedudantParenthesis cop while linting the file, with the following error message:

Inspecting 1 file
An error occurred while Style/RedundantParentheses cop was inspecting /path/to/test.rb.
To see the complete backtrace run rubocop -d.
.

1 file inspected, no offenses detected

1 error occurred:
An error occurred while Style/RedundantParentheses cop was inspecting /path/to/test.rb.
Errors are usually caused by RuboCop bugs.
Please, report your problems to RuboCop's issue tracker.
Mention the following information in the issue report:
0.40.0 (using Parser 2.3.1.0, running on ruby 2.3.1 x86_64-darwin15)

Steps to reproduce the problem

1. Create a test file with the following content:

   def foo(bar)
     (bar || ()).nil?
   end

2. Run rubocop test.rb

RuboCop version

$ rubocop -V
0.40.0 (using Parser 2.3.1.0, running on ruby 2.3.1 x86_64-darwin15)

[amencarini]

Just encountered the same issue.
The -d run adds the following:

Scanning /Users/amencarini/Projects/ruby/test_file.rb
An error occurred while Style/RedundantParentheses cop was inspecting /Users/amencarini/Projects/ruby/test_file.rb.
undefined method `hash_type?' for nil:NilClass
/Users/amencarini/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/rubocop-0.40.0/lib/rubocop/cop/style/redundant_parentheses.rb:41:in `parens_allowed?'
/Users/amencarini/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/rubocop-0.40.0/lib/rubocop/cop/style/redundant_parentheses.rb:30:in `on_begin'
/Users/amencarini/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/rubocop-0.40.0/lib/rubocop/cop/commissioner.rb:42:in `block (2 levels) in on_begin'