undefined method `source' for nil:NilClass in ZeroLengthPredicate

[chronodm]

Expected behavior

rubocop -a completes without errors

Actual behavior

rubocop -a bails after parsing five of 20 files, with the attached stack trace (originating at zero_length_predicate.rb:65).

Steps to reproduce the problem

Run rubocop -a against the following source:

class Foo
  attr_accessor :size

  def frob
    return nil if size == 0
    1
  end
end

Notes

• Using @size instead of size fixes the problem, as does using size <= 0 instead of size == 0.
• Using self.size instead of size does not fix the problem -- though self.size gets autocorrected to size before it fails.
• Introducing an empty? method does not fix the problem (although it's likely that in that case the failure is in the empty? method's own size == 0 check).
• adding # rubocop:disable Style/ZeroLengthPredicate after def frob, surprisingly, does not fix the problem.

RuboCop version

Include the output of rubocop -V:

$ bundle exec rubocop -V
0.40.0 (using Parser 2.3.1.0, running on ruby 2.2.3 x86_64-darwin14)

[tejasbubane]

Actually the bug is with the cop showing offense for size == 0:

Offenses:

rubocop_bug_test.rb:5:19: C: Style/ZeroLengthPredicate: Use empty? instead of size == 0.
    return nil if size == 0
                  ^^^^^^^^^

1 file inspected, 1 offense detected
Finished in 0.23116467497311532 seconds

This should not happen since the cop works on Array#size and not variables. Same happens for length. I added some failing specs for these and will send a PR soon.