Fix an error for Rails/FindEach

Follow up to rubocop#552 (comment).

This PR fixes an error for `Rails/FindEach` when using `where` with no receiver.

changelog/fix_an_error_for_rails_find_each.md

@@ -0,0 +1 @@
+* [#573](https://github.com/rubocop/rubocop-rails/pull/573): Fix an error for `Rails/FindEach` when using `where` with no receiver. ([@koic][])

lib/rubocop/cop/rails/find_each.rb

@@ -55,6 +55,8 @@ def active_model_error_where?(node)
         end
 
         def active_model_error?(node)
+          return false if node.nil?
+
           node.send_type? && node.method?(:errors)
         end
       end

spec/rubocop/cop/rails/find_each_spec.rb

@@ -45,7 +45,18 @@
   # Active Model Errors slice from the new query interface introduced in Rails 6.1.
   it 'does not register an offense when using `model.errors.where`' do
     expect_no_offenses(<<~RUBY)
-      model.errors.where(:title).each { |error| do_something(error)  }
+      class Model < ApplicationRecord
+        model.errors.where(:title).each { |error| do_something(error)  }
+      end
+    RUBY
+  end
+
+  it 'registers an offense when using `where` with no receiver' do
+    expect_offense(<<~RUBY)
+      class Model < ApplicationRecord
+        where(record: [record1, record2]).each(&:touch)
+                                          ^^^^ Use `find_each` instead of `each`.
+      end
     RUBY
   end