It appears that the checkstyleNohttp task doesn't run with a consistent working directory. As a result, the relative file references in src/nohttp/checkstyle don't work reliably. We're seeing intermittent failures on CI like this:
Unable to create Root Module: config {/tmp/build/6da1d659/git-repo/src/nohttp/checkstyle.xml}, classpath {/root/.gradle/caches/modules-2/files-2.1/io.spring.nohttp/nohttp-checkstyle/0.0.6.RELEASE/3196395cb9bb81d83d9d2cf376a738feb215ac91/nohttp-checkstyle-0.0.6.RELEASE.jar:/root/.gradle/caches/modules-2/files-2.1/com.puppycrawl.tools/checkstyle/8.37/a9b271f5bd253eccaa0b8c2b0f973e926e1980b4/checkstyle-8.37.jar:/root/.gradle/caches/modules-2/files-2.1/info.picocli/picocli/4.5.2/265314f98a6e7beed510f3bd7b5eaf1bfcaf9d50/picocli-4.5.2.jar:/root/.gradle/caches/modules-2/files-2.1/antlr/antlr/2.7.7/83cd2cd674a217ade95a4bb83a8a14f351f48bd0/antlr-2.7.7.jar:/root/.gradle/caches/modules-2/files-2.1/org.antlr/antlr4-runtime/4.8-1/2d0456a791f3a95916c8c23b3bea3a90eea24720/antlr4-runtime-4.8-1.jar:/root/.gradle/caches/modules-2/files-2.1/commons-beanutils/commons-beanutils/1.9.4/d52b9abcd97f38c81342bb7e7ae1eee9b73cba51/commons-beanutils-1.9.4.jar:/root/.gradle/caches/modules-2/files-2.1/com.google.guava/guava/29.0-jre/801142b4c3d0f0770dd29abea50906cacfddd447/guava-29.0-jre.jar:/root/.gradle/caches/modules-2/files-2.1/org.reflections/reflections/0.9.12/1c9d44c563eebe9b8a3afebd29ed5c4646db800c/reflections-0.9.12.jar:/root/.gradle/caches/modules-2/files-2.1/net.sf.saxon/Saxon-HE/10.3/43728f10ed9fc26ff5c71f27be9e8d7f60c10d4c/Saxon-HE-10.3.jar:/root/.gradle/caches/modules-2/files-2.1/io.spring.nohttp/nohttp/0.0.6.RELEASE/e66bc73bcd84ab727a2287b35ddd9708d9a03920/nohttp-0.0.6.RELEASE.jar:/root/.gradle/caches/modules-2/files-2.1/commons-collections/commons-collections/3.2.2/8ad72fe39fa8c91eaaf12aadb21e0c3661fe26d5/commons-collections-3.2.2.jar:/root/.gradle/caches/modules-2/files-2.1/com.google.guava/failureaccess/1.0.1/1dcf1de382a0bf95a3d8b0849546c88bac1292c9/failureaccess-1.0.1.jar:/root/.gradle/caches/modules-2/files-2.1/com.google.guava/listenablefuture/9999.0-empty-to-avoid-conflict-with-guava/b421526c5f297295adef1c886e5246c39d4ac629/listenablefuture-9999.0-empty-to-avoid-conflict-with-guava.jar:/root/.gradle/caches/modules-2/files-2.1/com.google.code.findbugs/jsr305/3.0.2/25ea2e8b0c338a877313bd4672d3fe056ea78f0d/jsr305-3.0.2.jar:/root/.gradle/caches/modules-2/files-2.1/org.checkerframework/checker-qual/2.11.1/8c43bf8f99b841d23aadda6044329dad9b63c185/checker-qual-2.11.1.jar:/root/.gradle/caches/modules-2/files-2.1/com.google.errorprone/error_prone_annotations/2.3.4/dac170e4594de319655ffb62f41cbd6dbb5e601e/error_prone_annotations-2.3.4.jar:/root/.gradle/caches/modules-2/files-2.1/com.google.j2objc/j2objc-annotations/1.3/ba035118bc8bac37d7eff77700720999acd9986d/j2objc-annotations-1.3.jar:/root/.gradle/caches/modules-2/files-2.1/org.javassist/javassist/3.26.0-GA/bb2890849968d8d8311ffba8c37b0ce16ce284dc/javassist-3.26.0-GA.jar:/root/.gradle/caches/modules-2/files-2.1/ch.qos.logback/logback-classic/1.2.3/7c4f3c474fb2c041d8028740440937705ebb473a/logback-classic-1.2.3.jar:/root/.gradle/caches/modules-2/files-2.1/ch.qos.logback/logback-core/1.2.3/864344400c3d4d92dfeb0a305dc87d953677c03c/logback-core-1.2.3.jar}.
> cannot initialize module SuppressionFilter - Unable to find: src/nohttp/suppressions.xml
> Unable to find: src/nohttp/suppressions.xml
> /root/.gradle/daemon/6.8.3/src/nohttp/suppressions.xml (No such file or directory)
It's looking for the suppressions file at /root/.gradle/daemon/6.8.3/src/nohttp/suppressions.xml. It should be using /tmp/build/6da1d659/git-repo/src/nohttp/suppressions.xml.