Fix an error for Rails/NotNullColumn when the block for change_table is empty

changelog/fix_error_for_rails_not_null_column.md

@@ -0,0 +1 @@
+* [#1299](https://github.com/rubocop/rubocop-rails/pull/1299): Fix an error for `Rails/NotNullColumn` when the block for `change_table` is empty. ([@earlopain][])

lib/rubocop/cop/rails/not_null_column.rb

@@ -136,6 +136,8 @@ def check_add_reference_in_change_table(node, table)
 
         def check_change_table(node)
           change_table?(node) do |table|
+            next unless node.body
+
             children = node.body.begin_type? ? node.body.children : [node.body]
             children.each do |child|
               check_add_column_in_change_table(child, table)

spec/rubocop/cop/rails/not_null_column_spec.rb

@@ -85,6 +85,17 @@ def change
         end
       RUBY
     end
+
+    it 'does not register an offense when the block is empty' do
+      expect_no_offenses(<<~RUBY)
+        class ExampleMigration < ActiveRecord::Migration[7.0]
+          def change
+            change_table :invoices do |t|
+            end
+          end
+        end
+      RUBY
+    end
   end
 
   context 'with change_table call' do