I just tried a full compile (mvn clean install) of errai-demos/errai-jpa-demo-todo-list on the 2.4 branch. The compile completed successfully. Is it possible that you have made some changes to the project on your end?
Looking at the Guava 13.0.1 source code, the @Nullable annotation referred to in the error message should be a javax.annotation.Nullable. This comes from the javax.annotation:jsr250-api:jar:1.0:provided dependency which is included in the demo's pom.