fix compaction path util npe (#15653)

Author: shuwenwei

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/compaction/execute/utils/CompactionPathUtils.java

@@ -38,7 +38,8 @@ public static PartialPath getPath(IDeviceID device, String measurement)
       String[] nodes = new String[device.segmentNum() + tableNameSegments.length];
       System.arraycopy(tableNameSegments, 0, nodes, 0, tableNameSegments.length);
       for (int i = 0; i < device.segmentNum() - 1; i++) {
-        nodes[i + tableNameSegments.length] = device.segment(i + 1).toString();
+        nodes[i + tableNameSegments.length] =
+            device.segment(i + 1) == null ? null : device.segment(i + 1).toString();
       }
       nodes[device.segmentNum() + tableNameSegments.length - 1] = measurement;
       MeasurementPath path = new MeasurementPath(nodes);

iotdb-core/datanode/src/test/java/org/apache/iotdb/db/storageengine/dataregion/compaction/utils/CompactionUtilsTest.java

@@ -0,0 +1,57 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.iotdb.db.storageengine.dataregion.compaction.utils;
+
+import org.apache.iotdb.commons.exception.MetadataException;
+import org.apache.iotdb.commons.path.PartialPath;
+import org.apache.iotdb.db.exception.StorageEngineException;
+import org.apache.iotdb.db.storageengine.dataregion.compaction.AbstractCompactionTest;
+import org.apache.iotdb.db.storageengine.dataregion.compaction.execute.utils.CompactionPathUtils;
+
+import org.apache.tsfile.exception.write.WriteProcessException;
+import org.apache.tsfile.file.metadata.IDeviceID;
+import org.apache.tsfile.file.metadata.StringArrayDeviceID;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.io.IOException;
+
+public class CompactionUtilsTest extends AbstractCompactionTest {
+  @Override
+  public void setUp()
+      throws IOException, WriteProcessException, MetadataException, InterruptedException {
+    super.setUp();
+  }
+
+  @Override
+  public void tearDown() throws IOException, StorageEngineException {
+    super.tearDown();
+  }
+
+  @Test
+  public void testCompactionPathUtils() {
+    try {
+      IDeviceID deviceID = new StringArrayDeviceID(new String[] {"db.table1", null, "tag1"});
+      PartialPath path = CompactionPathUtils.getPath(deviceID, "s1");
+    } catch (Exception e) {
+      Assert.fail();
+    }
+  }
+}