Add tryWithEngineOrNull

server/src/main/java/org/elasticsearch/action/admin/indices/flush/FlushRequest.java

@@ -45,16 +45,16 @@ public FlushRequest(StreamInput in) throws IOException {
     }
 
     /**
-     * Returns {@code true} iff a flush should block
-     * if a another flush operation is already running. Otherwise {@code false}
+     * Returns {@code true} iff a flush should block (e.g., if the engine is being reset or
+     * if a another flush operation is already running). Otherwise {@code false}
      */
     public boolean waitIfOngoing() {
         return this.waitIfOngoing;
     }
 
     /**
-     * if set to {@code true} the flush will block
-     * if a another flush operation is already running until the flush can be performed.
+     * if set to {@code true} the flush will block (e.g., if the engine is being reset or
+     * if a another flush operation is already running) until the flush can be performed.
      * The default is <code>true</code>
      */
     public FlushRequest waitIfOngoing(boolean waitIfOngoing) {