Wicket ExtJS project does not build with Java 8

Steps to reproduce
1) Get source from https://wicket-extjs-integration.googlecode.com/svn/trunk
2) mvn clean install with Java 8

Building the Wicket-ExtJS project with Java 8 fails witht he following error on aspectj:

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[ERROR] Failed to execute goal org.codehaus.mojo:aspectj-maven-plugin:1.3:compile (default) on project wicket-extjs: Compiler errors:
[ERROR] error at (no source information available)
[ERROR] /var/lib/jenkins/workspace/org_7.09_folder_java8/org_7.xx_wicket-extjs-parent_java8/core/src/main/java/org/wicketstuff/js/ext/AbstractExtButton.java:0::0 Internal compiler error
[ERROR] org.aspectj.apache.bcel.classfile.ClassFormatException: File: 'java/lang/CharSequence.class': Invalid byte tag in constant pool: 18