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

changelog/fix_error_rails_bulk_change_table.md

@@ -0,0 +1 @@
+* [#1335](https://github.com/rubocop/rubocop-rails/pull/1335): Fix an error for `Rails/BulkChangeTable` when the block for `change_table` is empty. ([@earlopain][])

lib/rubocop/cop/rails/bulk_change_table.rb

@@ -140,9 +140,9 @@ def on_send(node)
           return unless support_bulk_alter?
           return unless node.command?(:change_table)
           return if include_bulk_options?(node)
-          return unless node.block_node
+          return unless (body = node.block_node&.body)
 
-          send_nodes = send_nodes_from_change_table_block(node.block_node.body)
+          send_nodes = send_nodes_from_change_table_block(body)
 
           add_offense_for_change_table(node) if count_transformations(send_nodes) > 1
         end

spec/rubocop/cop/rails/bulk_change_table_spec.rb

@@ -25,6 +25,25 @@ def change
     end
   end
 
+  shared_examples 'wrong arguments' do
+    it 'does not register an offense for `change_table` with no block' do
+      expect_no_offenses(<<~RUBY)
+        def up
+          change_table(:users)
+        end
+      RUBY
+    end
+
+    it 'does not register an offense for `change_table` with empty block' do
+      expect_no_offenses(<<~RUBY)
+        def up
+          change_table(:users) do
+          end
+        end
+      RUBY
+    end
+  end
+
   shared_examples 'no offense' do
     it 'does not register an offense when including combinable transformations' do
       expect_no_offenses(<<~RUBY)
@@ -45,6 +64,8 @@ def change
         end
       RUBY
     end
+
+    it_behaves_like 'wrong arguments'
   end
 
   shared_examples 'offense for mysql' do
@@ -91,6 +112,8 @@ def change
         end
       RUBY
     end
+
+    it_behaves_like 'wrong arguments'
   end
 
   shared_examples 'offense for postgresql' do
@@ -153,6 +176,8 @@ def change
         end
       RUBY
     end
+
+    it_behaves_like 'wrong arguments'
   end
 
   it_behaves_like 'no offense'