Clover failing with "No Clover database found, skipping report generation" - maven

Question

I'm trying to add Clover to my maven (groovy) project in order to get some code coverage results. However it fails to generate the code coverage report.
The report is just empty.
My src files are located in src/main/groovy and my tests are located in src/test/groovy
When I run:
mvn clean clover:setup test clover:instrument clover:aggregate clover:clover
Build log:
[INFO] No Clover instrumentation done on source files in: [/home/xxx/workspace/yyy/src/main/java, /home/xxx/workspace/yyy/target/generated-sources/groovy-stubs/main] as no matching sources files found (JAVA_LANGUAGE)
[INFO] No Clover instrumentation done on source files in: [/home/xxx/workspace/yyy/src/test/java, /home/xxx/workspace/yyy/src/test/groovy] as no matching sources files found (JAVA_LANGUAGE)
...
[WARNING] No Clover database found, skipping report generation
[INFO] No report being generated for this module.
...
And indeed if I look in my tree for any database file,
My pom.xml:
....
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-enforcer-plugin</artifactId>
<version>1.0.1</version>
<executions>
<execution>
<id>enforce-versions</id>
<goals>
<goal>enforce</goal>
</goals>
</execution>
</executions>
<configuration>
<rules>
<AlwaysPass />
</rules>
<fail>true</fail>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.5.1</version>
</plugin>
<plugin>
<artifactId>maven-resources-plugin</artifactId>
<version>3.0.2</version>
<executions>
<execution>
<id>copy-test-resources</id>
<phase>validate</phase>
<goals>
<goal>testResources</goal>
</goals>
<configuration>
<resources>
<resource>
<directory>${project.basedir}</directory>
<filtering>true</filtering>
<includes>
<include>src/**/*.*</include>
<include>vars/**/*.*</include>
<include>resources/**/*.*</include>
</includes>
</resource>
</resources>
</configuration>
</execution>
</executions>
</plugin>
<!-- clover -->
<plugin>
<groupId>org.openclover</groupId>
<artifactId>clover-maven-plugin</artifactId>
<version>4.2.0</version>
</plugin>
<!-- Tests -->
<plugin>
<groupId>org.codehaus.gmavenplus</groupId>
<artifactId>gmavenplus-plugin</artifactId>
<version>1.6</version>
<executions>
<execution>
<goals>
<goal>addSources</goal>
<goal>addTestSources</goal>
<goal>generateStubs</goal>
<goal>compile</goal>
<goal>generateTestStubs</goal>
<goal>compileTests</goal>
</goals>
</execution>
</executions>
<configuration>
<sources>
<source>
<directory>${project.basedir}/src</directory>
<includes>
<include>**/*.groovy</include>
</includes>
</source>
</sources>
<testSources>
<source>
<directory>${project.basedir}/src/test/groovy</directory>
<includes>
<include>**/*.groovy</include>
</includes>
</source>
</testSources>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.20</version>
<configuration>
<failIfNoTests>true</failIfNoTests>
<includes>
<include>**/*</include>
</includes>
</configuration>
<executions>
<execution>
<id>test</id>
<phase>test</phase>
<goals>
<goal>test</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
<reporting>
<plugins>
<plugin>
<groupId>org.openclover</groupId>
<artifactId>clover-maven-plugin</artifactId>
<version>4.2.0</version>
</plugin>
</plugins>
</reporting>
</project>