Fix an error for Rails/WhereNot without second argument

This is basically rubocop#401 again, and a bit of rubocop#1321

changelog/fix_error_rails_where_not_no_second_argument.md

@@ -0,0 +1 @@
+* [#1330](https://github.com/rubocop/rubocop-rails/pull/1330): Fix an error for `Rails/WhereNot` when using placeholder without second argument. ([@earlopain][])

lib/rubocop/cop/rails/where_not.rb

@@ -43,10 +43,10 @@ def on_send(node)
 
             range = offense_range(node)
 
-            column_and_value = extract_column_and_value(template_node, value_node)
-            return unless column_and_value
+            column, value = extract_column_and_value(template_node, value_node)
+            return unless value
 
-            good_method = build_good_method(node.loc.dot&.source, *column_and_value)
+            good_method = build_good_method(node.loc.dot&.source, column, value)
             message = format(MSG, good_method: good_method)
 
             add_offense(range, message: message) do |corrector|
@@ -72,9 +72,9 @@ def extract_column_and_value(template_node, value_node)
           value =
             case template_node.value
             when NOT_EQ_ANONYMOUS_RE, NOT_IN_ANONYMOUS_RE
-              value_node.source
+              value_node&.source
             when NOT_EQ_NAMED_RE, NOT_IN_NAMED_RE
-              return unless value_node.hash_type?
+              return unless value_node&.hash_type?
 
               pair = value_node.pairs.find { |p| p.key.value.to_sym == Regexp.last_match(2).to_sym }
               pair.value.source

spec/rubocop/cop/rails/where_not_spec.rb

@@ -12,6 +12,12 @@
     RUBY
   end
 
+  it 'registers no offense when using `!=` and anonymous placeholder without second argument' do
+    expect_no_offenses(<<~RUBY)
+      User.where('name != ?')
+    RUBY
+  end
+
   it 'registers an offense and corrects when using `!=` and anonymous placeholder with safe navigation' do
     expect_offense(<<~RUBY)
       User&.where('name != ?', 'Gabe')
@@ -89,6 +95,12 @@
     RUBY
   end
 
+  it 'registers no offense when using `NOT IN` and named placeholder without second argument' do
+    expect_no_offenses(<<~RUBY)
+      User.where("name NOT IN (:names)")
+    RUBY
+  end
+
   it 'registers an offense and corrects when using `!=` and namespaced columns' do
     expect_offense(<<~RUBY)
       Course.where('enrollments.student_id != ?', student.id)