    java.lang.NullPointerException: Cannot invoke "String.equals(Object)" because "ts" is null
    	at org.hl7.fhir.r5.comparison.StructureDefinitionComparer.findInSliceList(StructureDefinitionComparer.java:606)
    	at org.hl7.fhir.r5.comparison.StructureDefinitionComparer.compareDiffChildren(StructureDefinitionComparer.java:554)
    	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.igtools.publisher.comparators.PreviousVersionComparator.finishChecks(PreviousVersionComparator.java:267)
    	at org.hl7.fhir.igtools.publisher.PublisherProcessor.checkConformanceResources(PublisherProcessor.java:1496)
    	at org.hl7.fhir.igtools.publisher.PublisherProcessor.loadConformance2(PublisherProcessor.java:104)
    	at org.hl7.fhir.igtools.publisher.Publisher.createIg(Publisher.java:403)
    	at org.hl7.fhir.igtools.publisher.Publisher.execute(Publisher.java:232)
    	at org.hl7.fhir.igtools.publisher.Publisher.main(Publisher.java:1594)