Merge pull request #17265 from hepin1989/fix-#17257

+act #17257 add Actor.ignoringBehavior

akka-actor/src/main/scala/akka/actor/Actor.scala

@@ -5,10 +5,11 @@
 package akka.actor
 
 import akka.AkkaException
+import akka.event.LoggingAdapter
+
 import scala.annotation.tailrec
 import scala.beans.BeanProperty
 import scala.util.control.NoStackTrace
-import akka.event.LoggingAdapter
 
 /**
  * INTERNAL API
@@ -340,6 +341,15 @@ object Actor {
     def apply(x: Any) = throw new UnsupportedOperationException("Empty behavior apply()")
   }
 
+  /**
+   * ignoringBehavior is a Receive-expression that consumes and ignores all messages.
+   */
+  @SerialVersionUID(1L)
+  object ignoringBehavior extends Receive {
+    def isDefinedAt(x: Any): Boolean = true
+    def apply(x: Any): Unit = ()
+  }
+
   /**
    * Default placeholder (null) used for "!" to indicate that there is no sender of the message,
    * that will be translated to the receiving system's deadLetters.
@@ -401,8 +411,6 @@ object Actor {
  */
 trait Actor {
 
-  import Actor._
-
   // to make type Receive known in subclasses without import
   type Receive = Actor.Receive