Fix an error for Style/NegatedIfElseCondition

changelog/fix_an_error_for_style_negated_if_else_condition.md

@@ -0,0 +1 @@
+* [#11646](https://github.com/rubocop/rubocop/pull/11646): Fix an error for `Style/NegatedIfElseCondition` when using `()` as a condition. ([@koic][])

lib/rubocop/cop/style/negated_if_else_condition.rb

@@ -48,13 +48,11 @@ def on_new_investigation
 
         def on_if(node)
           return unless if_else?(node)
-
-          condition = unwrap_begin_nodes(node.condition)
-
+          return unless (condition = unwrap_begin_nodes(node.condition))
           return if double_negation?(condition) || !negated_condition?(condition)
 
-          type = node.ternary? ? 'ternary' : 'if-else'
-          add_offense(node, message: format(MSG, type: type)) do |corrector|
+          message = message(node)
+          add_offense(node, message: message) do |corrector|
             unless corrected_ancestor?(node)
               correct_negated_condition(corrector, condition)
               swap_branches(corrector, node)
@@ -73,7 +71,8 @@ def if_else?(node)
         end
 
         def unwrap_begin_nodes(node)
-          node = node.children.first while node.begin_type? || node.kwbegin_type?
+          node = node.children.first while node && (node.begin_type? || node.kwbegin_type?)
+
           node
         end
 
@@ -82,6 +81,12 @@ def negated_condition?(node)
             (node.negation_method? || NEGATED_EQUALITY_METHODS.include?(node.method_name))
         end
 
+        def message(node)
+          type = node.ternary? ? 'ternary' : 'if-else'
+
+          format(MSG, type: type)
+        end
+
         def corrected_ancestor?(node)
           node.each_ancestor(:if).any? { |ancestor| @corrected_nodes&.include?(ancestor) }
         end

spec/rubocop/cop/style/negated_if_else_condition_spec.rb

@@ -229,6 +229,16 @@
     RUBY
   end
 
+  it 'does not crash when using `()` as a condition' do
+    expect_no_offenses(<<~RUBY)
+      if ()
+        foo
+      else
+        bar
+      end
+    RUBY
+  end
+
   it 'moves comments to correct branches during autocorrect' do
     expect_offense(<<~RUBY)
       if !condition.nil?