ST6RI-913 Exception opening .kermlx and .sysmlx files in editor

[seidewitz]

On of the updates in PR #734 was to move the OperandEList class to the org.omg.sysml.util package and re-implementation. This new implementation did not support the iterator method. However, when a .kermlx and .sysmlx file is opened in the Eclipse editor, iterator is called to get an iterator with which to iterate over the values of structural features. Even though the operands list is not included in XMI serialization, the system still calls iterate on the OperandEList for the operand structural feature, which resulted in a UnsupportedOperationException.

This PR updates EOperandList.iterator so that it returns the emptyIterator.

[himi]

It might be a different topic, but I found SysML2XMI sysml/src/validation/10-Analysis and Trades/10d-Dynamics Analysis.sysml failed with NullPointerException:

Transforming...
java.lang.NullPointerException: Cannot invoke "org.omg.sysml.lang.sysml.Feature.getChainingFeature()" because "feature" is null
	at org.omg.sysml.util.FeatureUtil.chainFeatures(FeatureUtil.java:404)
	at org.omg.sysml.adapter.FeatureAdapter.computeValueConnector(FeatureAdapter.java:825)
	at org.omg.sysml.adapter.UsageAdapter.computeValueConnector(UsageAdapter.java:214)
	at org.omg.sysml.adapter.FeatureAdapter.doTransform(FeatureAdapter.java:901)
	at org.omg.sysml.adapter.UsageAdapter.doTransform(UsageAdapter.java:223)
	at org.omg.sysml.adapter.ElementAdapter.transform(ElementAdapter.java:132)
	at org.omg.sysml.util.ElementUtil.transform(ElementUtil.java:379)
	at org.omg.sysml.util.ElementUtil.transformAll(ElementUtil.java:359)
	at org.omg.sysml.util.ElementUtil.transformAll(ElementUtil.java:363)
	at org.omg.sysml.util.ElementUtil.transformAll(ElementUtil.java:363)
	at org.omg.sysml.util.ElementUtil.transformAll(ElementUtil.java:363)
	at org.omg.sysml.util.ElementUtil.transformAll(ElementUtil.java:363)
	at org.omg.sysml.util.ElementUtil.transformAll(ElementUtil.java:353)
	at org.omg.sysml.util.SysMLUtil.transformAll(SysMLUtil.java:301)
	at org.omg.kerml.xtext.util.KerML2XMI.write(KerML2XMI.java:113)
	at org.omg.kerml.xtext.util.KerML2XMI.run(KerML2XMI.java:212)
	at org.omg.sysml.xtext.util.SysML2XMI.main(SysML2XMI.java:81)

[himi]

I confirmed it worked. Thank you.