Google AppEngine does not like leftshift

I ran into an issue last night where Google AppEngine wouldn’t persist my entities. If I create an entity using the parameters provided by Grails; then the Save operations would fail with the following error

Uncaught exception from servlet org.codehaus.groovy.runtime.InvokerInvocationException: groovy.lang.MissingMethodException: No signature of method: java.lang.StringBuilder.leftShift() is applicable for argument types: (org.codehaus.groovy.runtime.GStringImpl) values: [(login.email = ?1 )] at com.studentsonly.grails.plugins.uiperformance.CacheFilter.doFilter(CacheFilter.java:71) at com.google.apphosting.runtime.jetty.SaveSessionFilter.doFilter(SaveSessionFilter.java:35) at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43) at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.handle(AppVersionHandlerMap.java:237) at com.google.apphosting.runtime.jetty.RpcRequestParser.parseAvailable(RpcRequestParser.java:76) at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:139) at com.google.apphosting.runtime.JavaRuntime.handleRequest(JavaRuntime.java:235) at com.google.apphosting.base.RuntimePb$EvaluationRuntime$6.handleBlockingRequest(RuntimePb.java:4823) at com.google.apphosting.base.RuntimePb$EvaluationRuntime$6.handleBlockingRequest(RuntimePb.java:4821) at com.google.net.rpc.impl.BlockingApplicationHandler.handleRequest(BlockingApplicationHandler.java:24) at com.google.net.rpc.impl.RpcUtil.runRpcInApplication(RpcUtil.java:359) at com.google.net.rpc.impl.Server$2.run(Server.java:820) ...

The issue is described here. I tried their solution and it works fine for me.