Upgrading from 5.1 beta 2 to 5.1 stable

I just tried to upgrade from 5.1 beta 2 to the 5.1 stable release. When doing so I got the error below. I'm upgrading via tomcat with a Java 8 JDK.
First error:
First error:
- Code: Select all
org.apache.jasper.JasperException: Unable to compile class for JSP:
An error occurred at line: 1 in the generated java file
The type java.util.Map$Entry cannot be resolved. It is indirectly referenced from required .class files
Stacktrace:
org.apache.jasper.compiler.DefaultErrorHandler.javacError(DefaultErrorHandler.java:102)
org.apache.jasper.compiler.ErrorDispatcher.javacError(ErrorDispatcher.java:331)
org.apache.jasper.compiler.JDTCompiler.generateClass(JDTCompiler.java:469)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:378)