kevin@inspiron-15-5510:~/Desktop/check_style$ cat Test.java
import javax.swing.*;
import java.awt.*;
import java.util.function.Supplier;

public class Test {
   private final NotNullLazyValue<JComponent> myComponent = NotNullLazyValue.lazy(() -> {
      JPanel results = new JPanel(new GridBagLayout()) {};
       return results;
   });
}
class NotNullLazyValue<T> {
    public NotNullLazyValue() {
    }
    public static <T> NotNullLazyValue<T> lazy(Supplier<T> supplier) {
        return new NotNullLazyValue<>();
    }
}

kevin@inspiron-15-5510:~/Desktop/check_style$ javac Test.java

kevin@inspiron-15-5510:~/Desktop/check_style$ cat config.xml 
<?xml version="1.0"?>
<!DOCTYPE module PUBLIC "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN" "https://checkstyle.org/dtds/configuration_1_3.dtd">

<module name="Checker">
    <property name="charset" value="UTF-8" />
    <property name="severity" value="warning" />
    <property name="haltOnException" value="false" />

    <module name="TreeWalker">

        <module name="UnusedLocalVariable">
        </module>

    </module>
</module>

kevin@inspiron-15-5510:~/Desktop/check_style$ java -jar /home/kevin/Downloads/checkstyle-10.12.0-all.jar -c config.xml Test.java
Starting audit...
[ERROR] /home/kevin/Desktop/check_style/Test.java:1: Got an exception - java.lang.NullPointerException: Cannot invoke "com.puppycrawl.tools.checkstyle.api.DetailAST.getType()" because "parentAst" is null
        at com.puppycrawl.tools.checkstyle.checks.coding.UnusedLocalVariableCheck.getBlockContainingLocalAnonInnerClass(UnusedLocalVariableCheck.java:480)
        at com.puppycrawl.tools.checkstyle.checks.coding.UnusedLocalVariableCheck.visitLocalAnonInnerClass(UnusedLocalVariableCheck.java:404)
        at com.puppycrawl.tools.checkstyle.checks.coding.UnusedLocalVariableCheck.visitToken(UnusedLocalVariableCheck.java:312)
        at com.puppycrawl.tools.checkstyle.TreeWalker.notifyVisit(TreeWalker.java:335)
        at com.puppycrawl.tools.checkstyle.TreeWalker.processIter(TreeWalker.java:406)
        at com.puppycrawl.tools.checkstyle.TreeWalker.walk(TreeWalker.java:273)
        at com.puppycrawl.tools.checkstyle.TreeWalker.processFiltered(TreeWalker.java:154)
        at com.puppycrawl.tools.checkstyle.api.AbstractFileSetCheck.process(AbstractFileSetCheck.java:98)
        at com.puppycrawl.tools.checkstyle.Checker.processFile(Checker.java:334)
        at com.puppycrawl.tools.checkstyle.Checker.processFiles(Checker.java:293)
        at com.puppycrawl.tools.checkstyle.Checker.process(Checker.java:223)
        at com.puppycrawl.tools.checkstyle.Main.runCheckstyle(Main.java:415)
        at com.puppycrawl.tools.checkstyle.Main.runCli(Main.java:338)
        at com.puppycrawl.tools.checkstyle.Main.execute(Main.java:195)
        at com.puppycrawl.tools.checkstyle.Main.main(Main.java:130)
 [Checker]
Audit done.
Checkstyle ends with 1 errors.
kevin@inspiron-15-5510:~/Desktop/check_style$