checkstyle 10.3.3 and newer throws NullPointerException on annotated generic types from IllegalType rule

[motlin]

I minimized my repro to narrow down the cause.

The config:

❯ /bin/cat checkstyle-configuration.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">
    <module name="TreeWalker">
        <module name="IllegalType">
            <property name="illegalClassNames"
                    value="java.lang.StringBuffer, " />
        </module>
    </module>
</module>

The code:

❯ cat ExampleClass.java

package com.example;

import java.util.List;

import javax.validation.constraints.Pattern;

public class ExampleClass
{
    public void example(List<@Pattern String> strings)
    {
    }
}

❯ RUN_LOCALE="-Duser.language=en -Duser.country=US"
❯ java $RUN_LOCALE -jar checkstyle-10.3.3-all.jar -c checkstyle-configuration.xml ExampleClass.java 
Starting audit...
com.puppycrawl.tools.checkstyle.api.CheckstyleException: Exception was thrown while processing ExampleClass.java
	at com.puppycrawl.tools.checkstyle.Checker.processFiles(Checker.java:307)
	at com.puppycrawl.tools.checkstyle.Checker.process(Checker.java:224)
	at com.puppycrawl.tools.checkstyle.Main.runCheckstyle(Main.java:416)
	at com.puppycrawl.tools.checkstyle.Main.runCli(Main.java:339)
	at com.puppycrawl.tools.checkstyle.Main.execute(Main.java:196)
	at com.puppycrawl.tools.checkstyle.Main.main(Main.java:131)
Caused by: java.lang.NullPointerException: Cannot invoke "com.puppycrawl.tools.checkstyle.api.DetailAST.getLineNo()" because "ast" is null
	at com.puppycrawl.tools.checkstyle.api.AbstractCheck.log(AbstractCheck.java:276)
	at com.puppycrawl.tools.checkstyle.checks.coding.IllegalTypeCheck.checkIdent(IllegalTypeCheck.java:645)
	at com.puppycrawl.tools.checkstyle.checks.coding.IllegalTypeCheck.checkType(IllegalTypeCheck.java:674)
	at com.puppycrawl.tools.checkstyle.utils.TokenUtil.forEachChild(TokenUtil.java:244)
	at com.puppycrawl.tools.checkstyle.checks.coding.IllegalTypeCheck.checkTypeArguments(IllegalTypeCheck.java:719)
	at com.puppycrawl.tools.checkstyle.checks.coding.IllegalTypeCheck.checkType(IllegalTypeCheck.java:675)
	at com.puppycrawl.tools.checkstyle.checks.coding.IllegalTypeCheck.checkClassName(IllegalTypeCheck.java:633)
	at com.puppycrawl.tools.checkstyle.checks.coding.IllegalTypeCheck.visitParameterDef(IllegalTypeCheck.java:563)
	at com.puppycrawl.tools.checkstyle.checks.coding.IllegalTypeCheck.visitToken(IllegalTypeCheck.java:478)
	at com.puppycrawl.tools.checkstyle.TreeWalker.notifyVisit(TreeWalker.java:336)
	at com.puppycrawl.tools.checkstyle.TreeWalker.processIter(TreeWalker.java:407)
	at com.puppycrawl.tools.checkstyle.TreeWalker.walk(TreeWalker.java:274)
	at com.puppycrawl.tools.checkstyle.TreeWalker.processFiltered(TreeWalker.java:155)
	at com.puppycrawl.tools.checkstyle.api.AbstractFileSetCheck.process(AbstractFileSetCheck.java:98)
	at com.puppycrawl.tools.checkstyle.Checker.processFile(Checker.java:335)
	at com.puppycrawl.tools.checkstyle.Checker.processFiles(Checker.java:294)
	... 5 more
Checkstyle ends with 1 errors.

❯ java $RUN_LOCALE -jar checkstyle-10.3.2-all.jar -c checkstyle-configuration.xml ExampleClass.java
Starting audit...
Audit done.

---

Note that any little change to the config file prevents this problem. Even getting rid of the trailing comma or space at the end of StringBuffer in <property name="illegalClassNames" value="java.lang.StringBuffer, " /> prevents the problem.

---

[rnveach]

This issue is tied to #12017 and commits 3080013 and 01b7de6 and PRs #12034 and #12035.

Rationale was No need to trim strings here, they are trimmed further down in the method.

It appears it was not taken into account to have an extra comma on the end with an empty space. There is no exception if there is just an extra comma. The exception comes in when there is a space after the comma.

It is not user friendly to throw an exception. I think we should restore the code and drop the remaining empty item.

[romani]

We should restore trim.
As we do for all other.

Example: #12258

[nrmancuso]

On it

[romani]

Fix is merged