diff --git a/lib/fusuma/plugin/buffers/buffer.rb b/lib/fusuma/plugin/buffers/buffer.rb
index 600aad3..f9b2bfe 100644
--- a/lib/fusuma/plugin/buffers/buffer.rb
+++ b/lib/fusuma/plugin/buffers/buffer.rb
@@ -31,6 +31,11 @@ def buffer(event)
         def clear_expired(current_time: Time.now)
         end
 
+        # @return [TrueClass, FalseClass]
+        def empty?
+          @events.empty?
+        end
+
         # clear buffer
         def clear
           @events.clear
diff --git a/lib/fusuma/plugin/buffers/gesture_buffer.rb b/lib/fusuma/plugin/buffers/gesture_buffer.rb
index 5ce17b9..72de536 100644
--- a/lib/fusuma/plugin/buffers/gesture_buffer.rb
+++ b/lib/fusuma/plugin/buffers/gesture_buffer.rb
@@ -127,10 +127,6 @@ def gesture
           @events.last.record.gesture
         end
 
-        def empty?
-          @events.empty?
-        end
-
         def select_by_events(&block)
           return enum_for(:select_by_events) unless block
 
diff --git a/lib/fusuma/plugin/buffers/timer_buffer.rb b/lib/fusuma/plugin/buffers/timer_buffer.rb
index 441bced..e31863a 100644
--- a/lib/fusuma/plugin/buffers/timer_buffer.rb
+++ b/lib/fusuma/plugin/buffers/timer_buffer.rb
@@ -34,10 +34,6 @@ def clear_expired(current_time: Time.now)
             @events.delete(e)
           end
         end
-
-        def empty?
-          @events.empty?
-        end
       end
     end
   end