fix TsFileDeviceIterator

java/tsfile/src/main/java/org/apache/tsfile/read/LazyTsFileDeviceIterator.java

@@ -133,6 +133,10 @@ public IDeviceID next() {
     return currentDeviceAndMeasurementNodeOffsetPair.getLeft();
   }
 
+  public boolean hasCurrent() {
+    return this.currentDeviceAndMeasurementNodeOffsetPair != null;
+  }
+
   public IDeviceID getCurrentDeviceID() {
     if (currentDeviceAndMeasurementNodeOffsetPair == null) {
       throw new IllegalStateException("next() must be called before accessing current device");

java/tsfile/src/main/java/org/apache/tsfile/read/TsFileDeviceIterator.java

@@ -42,6 +42,9 @@ public TsFileDeviceIterator(
   }
 
   public Pair<IDeviceID, Boolean> current() throws IOException {
+    if (!lazyTsFileDeviceIterator.hasCurrent()) {
+      return null;
+    }
     return new Pair<>(
         lazyTsFileDeviceIterator.getCurrentDeviceID(),
         lazyTsFileDeviceIterator.isCurrentDeviceAligned());

java/tsfile/src/test/java/org/apache/tsfile/read/TsFileDeviceIteratorTest.java

@@ -73,6 +73,7 @@ public void test() throws IOException {
     int deviceFromIterator = 0;
     try (TsFileSequenceReader reader = new TsFileSequenceReader(FILE_PATH)) {
       TsFileDeviceIterator deviceIterator = reader.getAllDevicesIteratorWithIsAligned();
+      Assert.assertNull(deviceIterator.current());
       IDeviceID previous = null;
       while (deviceIterator.hasNext()) {
         Pair<IDeviceID, Boolean> next = deviceIterator.next();