From 134068f54a1ad1af85105860ff8672efb6feabfa Mon Sep 17 00:00:00 2001
From: Koichi ITO <koic.ito@gmail.com>
Date: Sat, 12 Sep 2020 15:59:57 +0900
Subject: [PATCH] [Fix #8704] Fix an error for `Lint/AmbiguousOperator`

Fixes #8704.

This PR fixes an error for `Lint/AmbiguousOperator`
when using safe navigation operator with a unary operator.
---
 CHANGELOG.md                                     | 1 +
 lib/rubocop/cop/lint/ambiguous_operator.rb       | 2 ++
 spec/rubocop/cop/lint/ambiguous_operator_spec.rb | 8 ++++++++
 3 files changed, 11 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index fe501e276fe..ae400d85be2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -30,6 +30,7 @@
 * [#8683](https://github.com/rubocop-hq/rubocop/issues/8683): Make naming cops work with non-ascii characters. ([@tejasbubane][])
 * [#8626](https://github.com/rubocop-hq/rubocop/issues/8626): Fix false negatives for `Lint/UselessMethodDefinition`. ([@marcandre][])
 * [#8698](https://github.com/rubocop-hq/rubocop/pull/8698): Fix cache to avoid encoding exception. ([@marcandre][])
+* [#8704](https://github.com/rubocop-hq/rubocop/issues/8704): Fix an error for `Lint/AmbiguousOperator` when using safe navigation operator with a unary operator. ([@koic][])
 
 ### Changes
 
diff --git a/lib/rubocop/cop/lint/ambiguous_operator.rb b/lib/rubocop/cop/lint/ambiguous_operator.rb
index 2df1285a861..338dc82c578 100644
--- a/lib/rubocop/cop/lint/ambiguous_operator.rb
+++ b/lib/rubocop/cop/lint/ambiguous_operator.rb
@@ -43,6 +43,8 @@ def on_new_investigation
             next unless diagnostic.reason == :ambiguous_prefix
 
             offense_node = find_offense_node_by(diagnostic)
+            next unless offense_node
+
             message = message(diagnostic)
 
             add_offense(
diff --git a/spec/rubocop/cop/lint/ambiguous_operator_spec.rb b/spec/rubocop/cop/lint/ambiguous_operator_spec.rb
index eb30f75b2e5..c8013d438d4 100644
--- a/spec/rubocop/cop/lint/ambiguous_operator_spec.rb
+++ b/spec/rubocop/cop/lint/ambiguous_operator_spec.rb
@@ -194,4 +194,12 @@
       end
     end
   end
+
+  context 'when using safe navigation operator with a unary operator' do
+    it 'does not register an offense' do
+      expect_no_offenses(<<~RUBY)
+        do_something&.* -1
+      RUBY
+    end
+  end
 end