SpaceInsideStringInterpolation cop fails with empty interpolation

[tfausak]

# example.rb
"#{}"

> rubocop -d example.rb

Inspecting 1 file
Scanning /private/tmp/example.rb
For /private/tmp: configuration from .../.gem/ruby/2.2.2/gems/rubocop-0.33.0/config/default.yml
Inheriting configuration from .../.gem/ruby/2.2.2/gems/rubocop-0.33.0/config/enabled.yml
Inheriting configuration from .../.gem/ruby/2.2.2/gems/rubocop-0.33.0/config/disabled.yml
An error occurred while Style/SpaceInsideStringInterpolation cop was inspecting /private/tmp/example.rb.
undefined method `loc' for nil:NilClass
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/lib/rubocop/cop/style/space_inside_string_interpolation.rb:24:in `block in on_dstr'
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/lib/rubocop/cop/style/space_inside_string_interpolation.rb:21:in `each'
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/lib/rubocop/cop/style/space_inside_string_interpolation.rb:21:in `on_dstr'
(eval):5:in `block (2 levels) in on_dstr'
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/lib/rubocop/cop/commissioner.rb:92:in `with_cop_error_handling'
(eval):4:in `block in on_dstr'
(eval):2:in `each'
(eval):2:in `on_dstr'
.../.gem/ruby/2.2.2/gems/ast-2.1.0/lib/ast/processor/mixin.rb:259:in `process'
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/lib/rubocop/cop/commissioner.rb:52:in `investigate'
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/lib/rubocop/cop/team.rb:33:in `inspect_file'
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/lib/rubocop/runner.rb:135:in `inspect_file'
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/lib/rubocop/runner.rb:106:in `block in do_inspection_loop'
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/lib/rubocop/runner.rb:100:in `loop'
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/lib/rubocop/runner.rb:100:in `do_inspection_loop'
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/lib/rubocop/runner.rb:78:in `process_file'
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/lib/rubocop/runner.rb:53:in `block in inspect_files'
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/lib/rubocop/runner.rb:51:in `each'
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/lib/rubocop/runner.rb:51:in `inspect_files'
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/lib/rubocop/runner.rb:30:in `run'
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/lib/rubocop/cli.rb:26:in `run'
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/bin/rubocop:13:in `block in <top (required)>'
.../.rubies/ruby-2.2.2/lib/ruby/2.2.0/benchmark.rb:303:in `realtime'
.../.gem/ruby/2.2.2/gems/rubocop-0.33.0/bin/rubocop:12:in `<top (required)>'
.../.gem/ruby/2.2.2/bin/rubocop:23:in `load'
.../.gem/ruby/2.2.2/bin/rubocop:23:in `<main>'
W

Offenses:

example.rb:2:2: W: Lint/EmptyInterpolation: Empty interpolation detected.
"#{}"
 ^^^

1 file inspected, 1 offense detected

1 error occurred:
An error occurred while Style/SpaceInsideStringInterpolation cop was inspecting /private/tmp/example.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:
0.33.0 (using Parser 2.2.2.6, running on ruby 2.2.2 x86_64-darwin14)
Finished in 0.023413064999658673 seconds

https://github.com/bbatsov/rubocop/blob/490c6af5068b61c0292ccc2850eabf6723cdd619/lib/rubocop/cop/style/space_inside_string_interpolation.rb#L22-L24