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

public class Test {
        List<String> list = List.of("a", "b", "c");
        List<String> newList = list.stream().map(_ -> "x").toList(); // violation
}
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="LambdaParameterName"/>
    </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:5:50: Name '_' must match pattern '^[a-z][a-zA-Z0-9]*$'. [LambdaParameterName]
Audit done.
Checkstyle ends with 1 errors.
PS D:\CS\test>