[Fix #1130] Fix crash for Rails/UniqueValidationWithoutIndex with bare validate

Author: jamiemccarthy

changelog/fix_bug_unique_validation_without_index.md

@@ -0,0 +1 @@
+* [#1130](https://github.com/rubocop/rubocop-rails/issues/1130): Fix crash for `Rails/UniqueValidationWithoutIndex` with bare validate. ([@jamiemccarthy][])

lib/rubocop/cop/rails/unique_validation_without_index.rb

@@ -125,7 +125,7 @@ def class_node(node)
 
         def uniqueness_part(node)
           pairs = node.arguments.last
-          return unless pairs.hash_type?
+          return unless pairs&.hash_type?
 
           pairs.each_pair.find do |pair|
             next unless pair.key.sym_type? && pair.key.value == :uniqueness

spec/rubocop/cop/rails/unique_validation_without_index_spec.rb

@@ -60,6 +60,24 @@ class User
           end
         RUBY
       end
+
+      it 'ignores a bare validates directive by itself' do
+        expect_no_offenses(<<~RUBY)
+          class User
+            validates
+          end
+        RUBY
+      end
+
+      it 'ignores a bare validates directive among others' do
+        expect_no_offenses(<<~RUBY)
+          class User
+            validates
+            after_commit :foo
+            def foo; true; end
+          end
+        RUBY
+      end
     end
 
     context 'when the table has an index but it is not unique' do