Some of Minitest Cops errors when used with minitest-power_assert

[tsugimoto]

Expected behavior

minitest-power_assert extends the #assert method, which would accept a block without arguments:

assert { 1 + 2 == 3 }

While this is not valid code in plain minitest and it is expected to either emit or not emit some warnings, RuboCop warns it in a rather surprising way.

Actual behavior

An error occurred while Minitest/AssertEmpty cop was inspecting /.../test/foo.rb:1:0.
undefined method `begin_type?' for nil:NilClass
/.../gems/rubocop-minitest-0.10.1/lib/rubocop/cop/mixin/minitest_cop_rule.rb:59:in `peel_redundant_parentheses_from'
/.../gems/rubocop-minitest-0.10.1/lib/rubocop/cop/mixin/minitest_cop_rule.rb:34:in `on_send'
/.../gems/rubocop-1.5.2/lib/rubocop/cop/commissioner.rb:100:in `public_send'
/.../gems/rubocop-1.5.2/lib/rubocop/cop/commissioner.rb:100:in `block (2 levels) in trigger_responding_cops'
/.../gems/rubocop-1.5.2/lib/rubocop/cop/commissioner.rb:166:in `with_cop_error_handling'

6 errors occurred:
An error occurred while Minitest/AssertEmpty cop was inspecting /.../test/foo.rb:1:0.
An error occurred while Minitest/AssertEqual cop was inspecting /.../test/foo.rb:1:0.
An error occurred while Minitest/AssertIncludes cop was inspecting /.../test/foo.rb:1:0.
An error occurred while Minitest/AssertInstanceOf cop was inspecting /.../test/foo.rb:1:0.
An error occurred while Minitest/AssertMatch cop was inspecting /.../test/foo.rb:1:0.
An error occurred while Minitest/AssertRespondTo cop was inspecting /.../test/foo.rb:1:0.
Errors are usually caused by RuboCop bugs.
Please, report your problems to RuboCop's issue tracker.
https://github.com/rubocop-hq/rubocop/issues

Steps to reproduce the problem

Inside a project configured to use rubocop-minitest, create a file test/foo.rb with content:

assert { 1 + 2 == 3 }

Then run:

$ rubocop test/foo.rb

RuboCop version

1.5.2 (using Parser 2.7.2.0, rubocop-ast 1.3.0, running on ruby 2.6.3 x86_64-darwin18)