This is the reason why there are empty tags in the XML files in the dataset.
first of all, what are empty Tags:
& <zhoz>& </ zhoz> this form, that is, there is no value in it
normal should be & < zhoz> 56 this form

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
 
# Move the xml with empty tags and move the corresponding images synchronously
import os
import xml.etree.ElementTree as ET
import shutil
 
origin_ann_dir = '/home/data_1/project/big-obj/RefineDet.PyTorch/data/VOCdevkit/VOC2007/Annotations/'# Set the original tag path to Annos
new_ann_dir = '/home/data_1/project/big-obj/RefineDet.PyTorch/data/VOCdevkit/VOC2007/xml-save/'# Set the new tag path Annotations
origin_pic_dir = '/home/data_1/project/big-obj/RefineDet.PyTorch/data/VOCdevkit/VOC2007/JPEGImages/'
new_pic_dir = '/home/data_1/project/big-obj/RefineDet.PyTorch/data/VOCdevkit/VOC2007/pic-save/'
k=0
p=0
q=0
for dirpaths, dirnames, filenames in os.walk(origin_ann_dir):  
  for filename in filenames:
    print("process...")
    k=k+1
    print(k)
    if os.path.isfile(r'%s%s' %(origin_ann_dir, filename)):   # get the absolute path to the original xml file, isfile() detects if it is a file isdir detects if it is a directory
      origin_ann_path = os.path.join(r'%s%s' %(origin_ann_dir, filename)) # If yes, get absolute path (repeat code)
      new_ann_path = os.path.join(r'%s%s' %(new_ann_dir, filename))
      tree = ET.parse(origin_ann_path)  
      root = tree.getroot()   
      if len(root.findall('object')):
        p=p+1
      else:
        print(filename)
        old_xml = origin_ann_dir + filename
        new_xml = new_ann_dir + filename
        old_pic = origin_pic_dir + filename.replace("xml","jpg")
        new_pic = new_pic_dir + filename.replace("xml","jpg")
        q=q+1
        shutil.move(old_pic, new_pic)
        shutil.move(old_xml, new_xml)
print("ok, ",p)
print("empty, ",q)

Found the XML file that generated the empty tag. The contents are as follows:

<annotation>
	<folder>obj1344</folder>
	<filename>obj1344_frame0000172.jpg</filename>
	<path>D:\Research\valid\obj1344\obj1344_frame0000172.jpg</path>
	<source>
		<database>Unknown</database>
	</source>
	<size>
		<width>480</width>
		<height>270</height>
		<depth>3</depth>
	</size>
	<segmented>0</segmented>
</annotation>

After the XML file is found, the image needs to be annotated again. After opening labelimg to annotate the data, the content of the XML file is as follows:

<annotation>
	<folder>JPEGImages</folder>
	<filename>obj1344_frame0000172.jpg</filename>
	<path>D:\new\SSD-master\datasets\VOC2007\JPEGImages\obj1344_frame0000172.jpg</path>
	<source>
		<database>Unknown</database>
	</source>
	<size>
		<width>480</width>
		<height>270</height>
		<depth>3</depth>
	</size>
	<segmented>0</segmented>
	<object>
		<name>plastic</name>
		<pose>Unspecified</pose>
		<truncated>1</truncated>
		<difficult>0</difficult>
		<bndbox>
			<xmin>181</xmin>
			<ymin>144</ymin>
			<xmax>355</xmax>
			<ymax>270</ymax>
		</bndbox>
	</object>
	<object>
		<name>timestamp</name>
		<pose>Unspecified</pose>
		<truncated>0</truncated>
		<difficult>0</difficult>
		<bndbox>
			<xmin>10</xmin>
			<ymin>5</ymin>
			<xmax>471</xmax>
			<ymax>43</ymax>
		</bndbox>
	</object>
	<object>
		<name>timestamp</name>
		<pose>Unspecified</pose>
		<truncated>1</truncated>
		<difficult>0</difficult>
		<bndbox>
			<xmin>14</xmin>
			<ymin>216</ymin>
			<xmax>480</xmax>
			<ymax>270</ymax>
		</bndbox>
	</object>
</annotation>

Modify and replace the original XML file to run.