LexicoHelper constructors are incorrect when explain option is set to true
The LexicoHelper class keeps track of the PBSolverDecorator used in the LexicoDecorator object. The object gathered when setting the xplain flag to true is not a PBSolverDecorator but an XplainPB. As such, an exception is launched when the explanation is enabled.
See here a trace of the error shown in p2cudf: org.sat4j.pb.tools.XplainPB cannot be cast to org.sat4j.pb.PBSolverDecorator Exception in thread "Thread-0" java.lang.NullPointerException at org.eclipse.equinox.p2.cudf.solver.Projector.stopSolver(Projector.java:490) at org.eclipse.equinox.p2.cudf.solver.SimplePlanner.stopSolver(SimplePlanner.java:61) at org.eclipse.equinox.p2.cudf.Main$1.run(Main.java:55)