[Fix rubocop#8771] Fix an error for Style/OneLineConditional

Fixes rubocop#8771.

This PR fixes an error for `Style/OneLineConditional` when using
`if-then-elsif-then-end`.

CHANGELOG.md

@@ -16,6 +16,7 @@
 * [#8754](https://github.com/rubocop-hq/rubocop/pull/8754): Fix an error for `Style/RandomWithOffset` when using a range with non-integer bounds. ([@eugeneius][])
 * [#8756](https://github.com/rubocop-hq/rubocop/issues/8756): Fix an infinite loop error for `Layout/EmptyLinesAroundAccessModifier` with `Layout/EmptyLinesAroundBlockBody` when using access modifier with block argument. ([@koic][])
 * [#8764](https://github.com/rubocop-hq/rubocop/issues/8764): Fix `Layout/CaseIndentation` not showing the cop name in output messages. ([@dvandersluis][])
+* [#8771](https://github.com/rubocop-hq/rubocop/issues/8771): Fix an error for `Style/OneLineConditional` when using `if-then-elsif-then-end`. ([@koic][])
 
 ### Changes
 

lib/rubocop/cop/style/one_line_conditional.rb

@@ -89,7 +89,9 @@ def multiline_replacement(node, indentation = nil)
         end
 
         def else_branch_to_multiline(else_branch, indentation)
-          if else_branch.if_type? && else_branch.elsif?
+          if else_branch.nil?
+            'end'
+          elsif else_branch.if_type? && else_branch.elsif?
             multiline_replacement(else_branch, indentation)
           else
             <<~RUBY.chomp

spec/rubocop/cop/style/one_line_conditional_spec.rb

@@ -179,6 +179,22 @@
       RUBY
     end
 
+    it 'registers and corrects an offense with multi-line construct for ' \
+       'if-then-elsif-then-end' do
+      expect_offense(<<~RUBY)
+        if cond1 then run elsif cond2 then maybe end
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ #{if_offense_message}
+      RUBY
+
+      expect_correction(<<~RUBY)
+        if cond1
+          run
+        elsif cond2
+          maybe
+        end
+      RUBY
+    end
+
     it 'registers and corrects an offense with multi-line construct for ' \
        'if-then-elsif-then-else-end' do
       expect_offense(<<~RUBY)