Resync should not send operations without sequence number

server/src/main/java/org/elasticsearch/index/shard/PrimaryReplicaSyncer.java

@@ -246,8 +246,8 @@ protected void doRun() throws Exception {
             Translog.Operation operation;
             while ((operation = snapshot.next()) != null) {
                 final long seqNo = operation.seqNo();
-                if (startingSeqNo >= 0 &&
-                    (seqNo == SequenceNumbers.UNASSIGNED_SEQ_NO || seqNo < startingSeqNo)) {
+                assert seqNo >= 0 : "resync should not send operation with unassigned sequence number [" + operation + "]";
+                if (seqNo < startingSeqNo) {
                     totalSkippedOps.incrementAndGet();
                     continue;
                 }

server/src/main/java/org/elasticsearch/index/translog/Translog.java

@@ -683,14 +683,8 @@ private Snapshot newMultiSnapshot(TranslogSnapshot[] snapshots) throws IOExcepti
     }
 
     private Stream<? extends BaseTranslogReader> readersAboveMinSeqNo(long minSeqNo) {
-        assert readLock.isHeldByCurrentThread() || writeLock.isHeldByCurrentThread() :
-            "callers of readersAboveMinSeqNo must hold a lock: readLock ["
-                + readLock.isHeldByCurrentThread() + "], writeLock [" + readLock.isHeldByCurrentThread() + "]";
-        return Stream.concat(readers.stream(), Stream.of(current))
-            .filter(reader -> {
-                final long maxSeqNo = reader.getCheckpoint().maxSeqNo;
-                return maxSeqNo == SequenceNumbers.UNASSIGNED_SEQ_NO || maxSeqNo >= minSeqNo;
-            });
+        assert readLock.isHeldByCurrentThread();
+        return Stream.concat(readers.stream(), Stream.of(current)).filter(reader -> reader.getCheckpoint().maxSeqNo >= minSeqNo);
     }
 
     /**