[Fix #7367] Fix an error for Style/OrAssignment

Fixes #7367.

This PR fixes an error for `Style/OrAssignment` cop
when `then` branch body is empty.

CHANGELOG.md

@@ -36,6 +36,7 @@
 * [#7361](https://github.com/rubocop-hq/rubocop/issues/7361): Fix a false positive for `Style/TernaryParentheses` when only the closing parenthesis is used in the last line of condition. ([@koic][])
 * [#7369](https://github.com/rubocop-hq/rubocop/issues/7369): Fix an infinite loop error for `Layout/IndentAssignment` with `Layout/IndentFirstArgument` when using multiple assignment. ([@koic][])
 * [#7177](https://github.com/rubocop-hq/rubocop/issues/7177), [#7370](https://github.com/rubocop-hq/rubocop/issues/7370): When correcting alignment, do not insert spaces into string literals. ([@buehmann][])
+* [#7367](https://github.com/rubocop-hq/rubocop/issues/7367): Fix an error for `Style/OrAssignment` cop when `then` branch body is empty. ([@koic][])
 
 ### Changes
 

lib/rubocop/cop/style/or_assignment.rb

@@ -81,7 +81,12 @@ def take_variable_and_default_from_ternary(node)
         end
 
         def take_variable_and_default_from_unless(node)
-          variable, default = *node.if_branch
+          if node.if_branch
+            variable, default = *node.if_branch
+          else
+            variable, default = *node.else_branch
+          end
+
           [variable, default]
         end
       end

spec/rubocop/cop/style/or_assignment_spec.rb

@@ -303,4 +303,22 @@
       RUBY
     end
   end
+
+  context 'when `then` branch body is empty' do
+    it 'registers an offense' do
+      expect_offense(<<~RUBY)
+        foo = nil
+        if foo
+        ^^^^^^ Use the double pipe equals operator `||=` instead.
+        else
+          foo = 2
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        foo = nil
+        foo ||= 2
+      RUBY
+    end
+  end
 end