diff --git a/client/src/main/java/com/github/dtprj/dongting/codec/DecoderCallbackCreator.java b/client/src/main/java/com/github/dtprj/dongting/codec/DecoderCallbackCreator.java
index 406727cd..369a1b85 100644
--- a/client/src/main/java/com/github/dtprj/dongting/codec/DecoderCallbackCreator.java
+++ b/client/src/main/java/com/github/dtprj/dongting/codec/DecoderCallbackCreator.java
@@ -22,9 +22,6 @@
 public interface DecoderCallbackCreator<T> {
     DecoderCallback<T> apply(DecodeContext ctx);
 
-    DecoderCallbackCreator<Void> VOID_DECODE_CALLBACK_CREATOR = fixed(DecoderCallback.VOID_DECODE_CALLBACK);
+    DecoderCallbackCreator<Void> VOID_DECODE_CALLBACK_CREATOR = ctx -> DecoderCallback.VOID_DECODE_CALLBACK;
 
-    static <T> DecoderCallbackCreator<T> fixed(DecoderCallback<T> c) {
-        return ctx -> c;
-    }
 }
diff --git a/client/src/main/java/com/github/dtprj/dongting/net/NioClient.java b/client/src/main/java/com/github/dtprj/dongting/net/NioClient.java
index 8ab61ccf..8c38e4de 100644
--- a/client/src/main/java/com/github/dtprj/dongting/net/NioClient.java
+++ b/client/src/main/java/com/github/dtprj/dongting/net/NioClient.java
@@ -135,11 +135,13 @@ public void waitStart() {
 
     public <T> CompletableFuture<ReadPacket<T>> sendRequest(WritePacket request,
                                                             DecoderCallbackCreator<T> decoder, DtTime timeout) {
+        Objects.requireNonNull(decoder);
         return sendRequest(null, request, decoder, timeout);
     }
 
     public <T> CompletableFuture<ReadPacket<T>> sendRequest(Peer peer, WritePacket request,
                                                             DecoderCallbackCreator<T> decoder, DtTime timeout) {
+        Objects.requireNonNull(decoder);
         CompletableFuture<ReadPacket<T>> f = new CompletableFuture<>();
         send(worker, peer, request, decoder, timeout, new RpcCallback<T>() {
             @Override
@@ -157,11 +159,13 @@ public void fail(Throwable ex) {
 
     public <T> void sendRequest(WritePacket request, DecoderCallbackCreator<T> decoder,
                                 DtTime timeout, RpcCallback<T> callback) {
+        Objects.requireNonNull(decoder);
         send(worker, null, request, decoder, timeout, callback);
     }
 
     public <T> void sendRequest(Peer peer, WritePacket request, DecoderCallbackCreator<T> decoder,
                                 DtTime timeout, RpcCallback<T> callback) {
+        Objects.requireNonNull(decoder);
         send(worker, peer, request, decoder, timeout, callback);
     }
 
diff --git a/server/src/main/java/com/github/dtprj/dongting/raft/impl/MemberManager.java b/server/src/main/java/com/github/dtprj/dongting/raft/impl/MemberManager.java
index 68f6f7f5..e1470411 100644
--- a/server/src/main/java/com/github/dtprj/dongting/raft/impl/MemberManager.java
+++ b/server/src/main/java/com/github/dtprj/dongting/raft/impl/MemberManager.java
@@ -701,8 +701,10 @@ public static boolean validCandidate(RaftStatusImpl raftStatus, int nodeId) {
     }
 
     public void transferLeadership(int nodeId, CompletableFuture<Void> f, DtTime deadline) {
-        groupConfig.getFiberGroup().fireFiber("transfer-leader",
-                new TranferLeaderFiberFrame(nodeId, f, deadline));
+        if (!groupConfig.getFiberGroup().fireFiber("transfer-leader",
+                new TranferLeaderFiberFrame(nodeId, f, deadline))) {
+            f.completeExceptionally(new RaftException("fire transfer leader fiber failed"));
+        }
     }
 
     private class TranferLeaderFiberFrame extends FiberFrame<Void> {
@@ -717,6 +719,13 @@ private class TranferLeaderFiberFrame extends FiberFrame<Void> {
             this.deadline = deadline;
         }
 
+        @Override
+        protected FrameCallResult handle(Throwable ex) {
+            RaftUtil.clearTransferLeaderCondition(raftStatus);
+            f.completeExceptionally(ex);
+            return Fiber.frameReturn();
+        }
+
         @Override
         public FrameCallResult execute(Void input) {
             if (raftStatus.getTransferLeaderCondition() != null) {
@@ -777,7 +786,7 @@ private FrameCallResult checkBeforeTransferLeader(Void v) {
                 req.groupId = groupId;
                 TransferLeaderReq.TransferLeaderReqWritePacket frame = new TransferLeaderReq.TransferLeaderReqWritePacket(req);
                 client.sendRequest(newLeader.getNode().getPeer(), frame,
-                                null, new DtTime(5, TimeUnit.SECONDS))
+                                DecoderCallbackCreator.VOID_DECODE_CALLBACK_CREATOR, new DtTime(5, TimeUnit.SECONDS))
                         .whenComplete((rf, ex) -> {
                             if (ex != null) {
                                 log.error("transfer leader failed, groupId={}", groupId, ex);