java.lang.NoClassDefFoundError: eu/solven/cleanthat/language/IEngineProperties

Start by reproducing the reported Maven plugin configuration with Java 21 and the cleanthat step enabled. Inspect how the cleanthat step is resolved and run the reported check goal; done means the configuration no longer fails with NoClassDefFoundError for eu/solven/cleanthat/language/IEngineProperties.

• summary of problem java.lang.NoClassDefFoundError
• Maven version 4.0.0.RC2
• spotless version: maven plugin 2.44.0.BETA4
• operating system and version Windows 64 Pro/Java 21

The maven config in my project like this.

<plugin>
    <groupId>com.diffplug.spotless</groupId>
    <artifactId>spotless-maven-plugin</artifactId>
    <version>2.44.0.BETA4</version>
    <configuration>
        <java>
            <!-- These are the defaults, you can override if you want -->
            <includes>
                <include>src/main/java/**/*.java</include>
                <include>src/test/java/**/*.java</include>
            </includes>

            <!-- Cleanthat will refactor your code, but it may break your style: apply it before your formatter -->
            <cleanthat/>

            <googleJavaFormat>
                <version>1.25.2</version>
                <style>AOSP</style>
                <reflowLongStrings>true</reflowLongStrings>
            </googleJavaFormat>
            <!-- <eclipse/>  -->
            <!-- <prettier/>   -->

            <importOrder/> 
            <removeUnusedImports/>
            <formatAnnotations/> 
        </java>
    </configuration>
    <executions>
        <execution>
            <goals>
                <goal>check</goal>
            </goals>
            <phase>compile</phase>
        </execution>
    </executions>
</plugin>

[INFO] Index file does not exist. Fallback to an empty index
[ERROR] Step 'cleanthat' found problem in 'ApplicationEvents.java':
eu/solven/cleanthat/language/IEngineProperties
java.lang.NoClassDefFoundError: eu/solven/cleanthat/language/IEngineProperties