Sometimes I get the following stacktrace when I try to get the tasks for a selection.
Only rebuilding seems to help:

org.spoofax.interpreter.core.InterpreterException: Exception during evaluation
at org.spoofax.interpreter.core.Interpreter.evaluate(Interpreter.java:120)
at org.spoofax.interpreter.core.Interpreter.invoke(Interpreter.java:82)
at org.strategoxt.HybridInterpreter.invoke(HybridInterpreter.java:442)
at org.strategoxt.imp.debug.core.str.launching.DebuggableHybridInterpreter.invoke(DebuggableHybridInterpreter.java:150)
at org.strategoxt.imp.runtime.services.StrategoObserver.invoke(StrategoObserver.java:637)
at org.strategoxt.imp.runtime.services.StrategoObserver.invoke(StrategoObserver.java:595)
at org.strategoxt.imp.runtime.services.menus.model.StrategoBuilder.invokeObserver(StrategoBuilder.java:334)
at org.strategoxt.imp.runtime.services.menus.model.StrategoBuilder.execute(StrategoBuilder.java:200)
at org.strategoxt.imp.runtime.services.menus.model.StrategoBuilder.access$1(StrategoBuilder.java:184)
at org.strategoxt.imp.runtime.services.menus.model.StrategoBuilder$1.run(StrategoBuilder.java:171)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:53)
Caused by: java.lang.NullPointerException
at org.metaborg.runtime.task.primitives.task_api_debug_info_0_1.createDebugTuple(task_api_debug_info_0_1.java:55)
at org.metaborg.runtime.task.primitives.task_api_debug_info_0_1.call(task_api_debug_info_0_1.java:37)
at org.spoofax.interpreter.stratego.PrimT.eval(PrimT.java:63)
at org.spoofax.interpreter.stratego.Strategy.evaluate(Strategy.java:76)
at org.spoofax.interpreter.stratego.SDefT.evaluate(SDefT.java:213)
at org.strategoxt.lang.InteropStrategy.invokeDynamic(InteropStrategy.java:57)
at org.strategoxt.lang.DynamicStrategy.invoke(DynamicStrategy.java:22)
at org.strategoxt.lang.SRTS_all.map(SRTS_all.java:60)
at org.strategoxt.lang.SRTS_all.invoke(SRTS_all.java:21)
at org.strategoxt.lang.compat.override.performance_tweaks.map_1_0_override.invoke(map_1_0_override.java:29)
at org.strategoxt.lang.Strategy.invokeDynamic(Strategy.java:40)
at org.strategoxt.lang.InteropSDefT.evaluate(InteropSDefT.java:192)
at org.strategoxt.lang.InteropSDefT.evaluate(InteropSDefT.java:183)
at org.strategoxt.lang.InteropSDefT$StrategyBody.evaluate(InteropSDefT.java:245)
at org.strategoxt.lang.InteropSDefT$StrategyBody.eval(InteropSDefT.java:238)
at org.spoofax.interpreter.stratego.Strategy.evaluate(Strategy.java:76)
at org.spoofax.interpreter.core.Interpreter.evaluate(Interpreter.java:109)
… 10 more
org.spoofax.interpreter.core.InterpreterException: Exception during evaluation
at org.spoofax.interpreter.core.Interpreter.evaluate(Interpreter.java:120)
at org.spoofax.interpreter.core.Interpreter.invoke(Interpreter.java:82)
at org.strategoxt.HybridInterpreter.invoke(HybridInterpreter.java:442)
at org.strategoxt.imp.debug.core.str.launching.DebuggableHybridInterpreter.invoke(DebuggableHybridInterpreter.java:150)
at org.strategoxt.imp.runtime.services.StrategoObserver.invoke(StrategoObserver.java:637)
at org.strategoxt.imp.runtime.services.StrategoObserver.invoke(StrategoObserver.java:595)
at org.strategoxt.imp.runtime.services.menus.model.StrategoBuilder.invokeObserver(StrategoBuilder.java:334)
at org.strategoxt.imp.runtime.services.menus.model.StrategoBuilder.execute(StrategoBuilder.java:200)
at org.strategoxt.imp.runtime.services.menus.model.StrategoBuilder.access$1(StrategoBuilder.java:184)
at org.strategoxt.imp.runtime.services.menus.model.StrategoBuilder$1.run(StrategoBuilder.java:171)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:53)
Caused by: java.lang.NullPointerException
at org.metaborg.runtime.task.primitives.task_api_debug_info_0_1.createDebugTuple(task_api_debug_info_0_1.java:55)
at org.metaborg.runtime.task.primitives.task_api_debug_info_0_1.call(task_api_debug_info_0_1.java:37)
at org.spoofax.interpreter.stratego.PrimT.eval(PrimT.java:63)
at org.spoofax.interpreter.stratego.Strategy.evaluate(Strategy.java:76)
at org.spoofax.interpreter.stratego.SDefT.evaluate(SDefT.java:213)
at org.strategoxt.lang.InteropStrategy.invokeDynamic(InteropStrategy.java:57)
at org.strategoxt.lang.DynamicStrategy.invoke(DynamicStrategy.java:22)
at org.strategoxt.lang.SRTS_all.map(SRTS_all.java:60)
at org.strategoxt.lang.SRTS_all.invoke(SRTS_all.java:21)
at org.strategoxt.lang.compat.override.performance_tweaks.map_1_0_override.invoke(map_1_0_override.java:29)
at org.strategoxt.lang.Strategy.invokeDynamic(Strategy.java:40)
at org.strategoxt.lang.InteropSDefT.evaluate(InteropSDefT.java:192)
at org.strategoxt.lang.InteropSDefT.evaluate(InteropSDefT.java:183)
at org.strategoxt.lang.InteropSDefT$StrategyBody.evaluate(InteropSDefT.java:245)
at org.strategoxt.lang.InteropSDefT$StrategyBody.eval(InteropSDefT.java:238)
at org.spoofax.interpreter.stratego.Strategy.evaluate(Strategy.java:76)
at org.spoofax.interpreter.core.Interpreter.evaluate(Interpreter.java:109)
… 10 more

Submitted by Arjen on 8 May 2014 at 16:41