Fix compilation error

Author: GalLalouche

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/async/AsyncExecutionId.java

@@ -10,6 +10,8 @@
 import org.elasticsearch.common.io.stream.ByteBufferStreamInput;
 import org.elasticsearch.common.io.stream.BytesStreamOutput;
 import org.elasticsearch.common.io.stream.StreamInput;
+import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.common.io.stream.Writeable;
 import org.elasticsearch.tasks.TaskId;
 
 import java.io.IOException;
@@ -20,7 +22,7 @@
 /**
  * A class that contains all information related to a submitted async execution.
  */
-public final class AsyncExecutionId {
+public final class AsyncExecutionId implements Writeable {
     public static final String ASYNC_EXECUTION_ID_HEADER = "X-Elasticsearch-Async-Id";
     public static final String ASYNC_EXECUTION_IS_RUNNING_HEADER = "X-Elasticsearch-Async-Is-Running";
 
@@ -115,4 +117,13 @@ public static AsyncExecutionId decode(String id) {
         }
         return new AsyncExecutionId(docId, new TaskId(taskId), id);
     }
+
+    @Override
+    public void writeTo(StreamOutput out) throws IOException {
+        out.writeString(getEncoded());
+    }
+
+    public static AsyncExecutionId readFrom(StreamInput input) throws IOException {
+        return decode(input.readString());
+    }
 }