Optional Variable Groups in AzimuthThrusterFeedback is not optional.

[THEvang]

When defining the variable group AzimuthThrusterFeedback, BladePitchand ShaftSpeed are not treated as optional elements. The following definition leads to an exception in osp-cli

<AzimuthThrusterFeedback name="main_propeller_port_feedback"> <AzimuthAngle name="main_propeller_port_azimuth"> <Variable ref="thruster_states.main_propeller_port.azimuth"/> </AzimuthAngle> <Force name="main_propeller_port_thrust"> <Variable ref="thruster_states.main_propeller_port.thrust"/> </Force> </AzimuthThrusterFeedback>

with the following exception:

Exception in thread "main" java.lang.NullPointerException at com.opensimulationplatform.modeldescription.xml.converter.tentative.BladePitchTypeConverter.convert(BladePitchTypeConverter.java:26) at com.opensimulationplatform.modeldescription.xml.converter.tentative.AzimuthThrusterFeedbackTypeConverter.convert(AzimuthThrusterFeedbackTypeConverter.java:28) at com.opensimulationplatform.modeldescription.xml.converter.tentative.AzimuthThrusterFeedbackTypeConverter.convert(AzimuthThrusterFeedbackTypeConverter.java:18) at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195) at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1654) at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484) at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474) at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913) at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578) at com.opensimulationplatform.modeldescription.xml.converter.Converter.convert(Converter.java:26) at com.opensimulationplatform.modeldescription.xml.converter.generic.GenericTypeConverter.convert(GenericTypeConverter.java:273) at com.opensimulationplatform.modeldescription.xml.converter.generic.GenericTypeConverter.convert(GenericTypeConverter.java:66) at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195) at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1654) at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484) at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474) at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913) at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578) at com.opensimulationplatform.modeldescription.xml.converter.Converter.convert(Converter.java:26) at com.opensimulationplatform.modeldescription.xml.converter.ospmodeldescriptiontype.OspModelDescriptionTypeConverter.convert(OspModelDescriptionTypeConverter.java:110) at com.opensimulationplatform.modeldescription.xml.factory.ModelDescriptionFactory.create(ModelDescriptionFactory.java:22) at com.opensimulationplatform.cli.Validator.validate(Validator.java:60) at com.opensimulationplatform.cli.Main.main(Main.java:85)