Docker build failed: Mockito cannot mock this class

[DaBonse]

Plugin Version 6.0.2 and 6.1.0

Keycloak Version: 26.1.2-2

Docker Base Image from https://quay.io/repository/keycloak/keycloak?tab=tags

Docker Build of Keycloak failed, because Plugin Tests failed with error:

`
[...]
44.74 [ERROR] HttpClientTest.postShouldThrowIfRequestThrows:264 Mockito
44.74 Mockito cannot mock this class: class org.apache.http.impl.client.HttpClientBuilder.
44.74
44.74 If you're not sure why you're getting this error, please open an issue on GitHub.
44.74
44.74
44.74 Java : 25
44.74 JVM vendor name : Eclipse Adoptium
44.74 JVM vendor version : 25+36-LTS
44.74 JVM name : OpenJDK 64-Bit Server VM
44.74 JVM version : 25+36-LTS
44.74 JVM info : mixed mode, sharing
44.74 OS name : Linux
44.74 OS version : 6.10.14-linuxkit
44.74
44.74
44.74 You are seeing this disclaimer because Mockito is configured to create inlined mocks.
44.74 You can learn about inline mocks and their limitations under item #39 of the Mockito class javadoc.
44.74
44.74 Underlying exception : org.mockito.exceptions.base.MockitoException: Could not modify all classes [class org.apache.http.impl.client.HttpClientBuilder, class java.lang.Object]
44.74 [INFO]
44.74 [ERROR] Tests run: 109, Failures: 0, Errors: 76, Skipped: 0
44.74 [INFO]
44.74 [INFO] ------------------------------------------------------------------------
44.74 [INFO] BUILD FAILURE
44.74 [INFO] ------------------------------------------------------------------------
44.74 [INFO] Total time: 42.887 s
44.74 [INFO] Finished at: 2025-09-30T00:56:53Z
44.74 [INFO] ------------------------------------------------------------------------
44.75 [ERROR] Failed to execute goal org.apache.maven.plugins:maven-surefire-plugin:3.5.3:test (default-test) on project keycloak-rest-provider:
44.75 [ERROR]
44.75 [ERROR] See /tmp/target/surefire-reports for the individual test results.
44.75 [ERROR] See dump files (if any exist) [date].dump, [date]-jvmRun[N].dump and [date].dumpstream.
44.75 [ERROR] -> [Help 1]
44.75 [ERROR]
44.75 [ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
44.75 [ERROR] Re-run Maven using the -X switch to enable full debug logging.
44.75 [ERROR]
44.75 [ERROR] For more information about the errors and possible solutions, please read the following articles:
44.75 [ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException

`

This is one example error, picked from the Docker logs. All errors have the same form