Maven plugin incompatible with 3.3.9

Summary of problem

Using the Spotless plugin in a Maven project and applying with Maven 3.3.9 throws an exception when I mvn spotless:check.

It looks like this is only in 1.21.1, this was fine in 1.20.0.

• Gradle or maven version - Maven 3.3.9
• spotless version - 1.21.1
• operating system and version - Macos 10.14.3
• copy-paste your full Spotless configuration block(s), and a link to a public git repo that reproduces the problem if possible

<plugin>
    <groupId>com.diffplug.spotless</groupId>
    <artifactId>spotless-maven-plugin</artifactId>
    <version>1.21.1</version>
    <executions>
        <execution>
            <id>check</id>
            <goals>
                <goal>check</goal>
            </goals>
        </execution>
    </executions>
    <configuration>
        <java>
            <eclipse>
                <version>4.10.0</version>
                <file>path/to/eclipse-formatter.xml</file>
            </eclipse>
            <importOrder>
                <file>path/to/java.importorder</file>
            </importOrder>
            <removeUnusedImports />
        </java>
        <formats>
            <format>
                <!-- XML files -->
                <includes>
                    <include>src/main/**/*.xml</include>
                    <include>**/pom.xml</include>
                </includes>
                <excludes>
                    <exclude>src/main/resources/rebel-remote.xml</exclude>
                    <exclude>src/main/resources/rebel.xml</exclude>
                    <exclude>**/target/**/pom.xml</exclude>
                </excludes>
                <indent>
                    <spaces>true</spaces>
                    <spacesPerTab>4</spacesPerTab>
                </indent>
                <trimTrailingWhitespace />
            </format>
            <format>
                <includes>
                    <!-- YAML -->
                    <include>src/main/**/*.yml</include>
                    <include>src/main/**/*.yaml</include>
                    <!-- JS within Java projects -->
                    <include>src/main/**/*.js</include>
                    <!-- SQL imports -->
                    <include>src/main/**/*.sql</include>
                </includes>
                <indent>
                    <spaces>true</spaces>
                    <spacesPerTab>2</spacesPerTab>
                </indent>
                <trimTrailingWhitespace />
            </format>
        </formats>
    </configuration>
</plugin>

• copy-paste the full content of any console errors emitted by gradlew spotless[Apply/Check] --stacktrace

https://gist.github.com/phillipuniverse/db14a796ffb4e8392da89c790537fd02

[nedtwigg]

@lutovich might be able to correct me, but it might be as simple as 3.5.2 was the version that he or I were using when we set up mvnw. But it should be 3.1.0 since we claim to support it.

[fvgh]

Exclusion of classworlds:classworlds did not fix the problem. Using the latest org.codehaus.plexus:plexus-resources version 1.2.0 (which does not depend on classworlds), did not fix the problem.

The problem is not deterministic. But it has been found with the latest version, that it only occurred with the install goal, but not when calling the spotless plugin goals directly. Hence it seems unlikely that the problem is caused by spotless. It is assumed that Maven 3.1.0 has a bug.

Original problem with Maven 3.3.9 was not reproducible with reasonable effort.