    java.lang.NullPointerException: Cannot invoke "java.util.List.iterator()" because "lc" is null
    	at org.hl7.fhir.r5.comparison.StructureDefinitionComparer.compareDiffChildren(StructureDefinitionComparer.java:553)
    	at org.hl7.fhir.r5.comparison.StructureDefinitionComparer.compareDiff(StructureDefinitionComparer.java:475)
    	at org.hl7.fhir.r5.comparison.StructureDefinitionComparer.compareDiffChildren(StructureDefinitionComparer.java:581)
    	at org.hl7.fhir.r5.comparison.StructureDefinitionComparer.compareDiff(StructureDefinitionComparer.java:475)
    	at org.hl7.fhir.r5.comparison.StructureDefinitionComparer.compare(StructureDefinitionComparer.java:179)
    	at org.hl7.fhir.r5.comparison.ComparisonSession.compare(ComparisonSession.java:107)
    	at org.hl7.fhir.r5.comparison.StructureDefinitionComparer.checkAddTypeUnion(StructureDefinitionComparer.java:966)
    	at org.hl7.fhir.r5.comparison.StructureDefinitionComparer.unionTypes(StructureDefinitionComparer.java:903)
    	at org.hl7.fhir.r5.comparison.StructureDefinitionComparer.compareElements(StructureDefinitionComparer.java:278)
    	at org.hl7.fhir.r5.comparison.StructureDefinitionComparer.compareChildren(StructureDefinitionComparer.java:382)
    	at org.hl7.fhir.r5.comparison.StructureDefinitionComparer.compareElements(StructureDefinitionComparer.java:295)
    	at org.hl7.fhir.r5.comparison.StructureDefinitionComparer.compare(StructureDefinitionComparer.java:173)
    	at org.hl7.fhir.r5.comparison.ComparisonSession.compare(ComparisonSession.java:107)
    	at org.hl7.fhir.igtools.publisher.comparators.IpaComparator.finishChecks(IpaComparator.java:232)
    	at org.hl7.fhir.igtools.publisher.Publisher.checkConformanceResources(Publisher.java:6588)
    	at org.hl7.fhir.igtools.publisher.Publisher.loadConformance2(Publisher.java:6392)
    	at org.hl7.fhir.igtools.publisher.Publisher.createIg(Publisher.java:1208)
    	at org.hl7.fhir.igtools.publisher.Publisher.execute(Publisher.java:1067)
    	at org.hl7.fhir.igtools.publisher.Publisher.main(Publisher.java:15577)
    	at org.hl7.fhir.igtools.web.PublicationProcess.runBuild(PublicationProcess.java:1080)
    	at org.hl7.fhir.igtools.web.PublicationProcess.doPublish(PublicationProcess.java:556)
    	at org.hl7.fhir.igtools.web.PublicationProcess.publishInner2(PublicationProcess.java:469)
    	at org.hl7.fhir.igtools.web.PublicationProcess.publishInner(PublicationProcess.java:286)
    	at org.hl7.fhir.igtools.web.PublicationProcess.publish(PublicationProcess.java:146)
    	at org.hl7.fhir.igtools.publisher.Publisher.main(Publisher.java:15325)