PS D:\CS\test> cat src/Test.java                                                
import java.util.PriorityQueue;
import java.util.Queue;

public class Test {
    void test() {
        Queue<Integer> q = new PriorityQueue<>();
        q.add(1);
        var _ = q.poll();
    }
}
PS D:\CS\test> cat config.xml                                                   
<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
        "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
        "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">
<module name="Checker">
    <property name="charset" value="UTF-8"/>
    <module name="TreeWalker">
         <module name="IllegalIdentifierName"/>
    </module>
</module>
PS D:\CS\test> java  -jar checkstyle-10.17.0-all.jar -c config.xml src/Test.java
Starting audit...
[ERROR] D:\CS\test\src\Test.java:8:13: Name '_' must match pattern '(?i)^(?!(record|yield|var|permits|sealed|_)$).+$'. [IllegalIdentifierName]
Audit done.
Checkstyle ends with 1 errors.
PS D:\CS\test>