Snapshot generation fails for extensions with value[x].code elements

[ashtty11]

Bug
Snapshot generation fails for extensions where the differential section contains elements one level down from Extension.value[x], for e.g. Extension.value[x].code

  {
    "id": "Extension.value[x]",
    "path": "Extension.value[x]",
    "min": 1,
    "type": [
      {
        "code": "Coding"
      }
    ]
  },
  {
    "id": "Extension.value[x].system",
    "path": "Extension.value[x].system",
    "min": 1
  },
  {
    "id": "Extension.value[x].code",
    "path": "Extension.value[x].code",
    "min": 1
  }

HAPI library tries to throw the following error

Extension.value[x] has children for type Coding in profile icd-10-gm-mehrfachcodierungs-kennzeichen but can't find type

But this error is not handled properly. It ends up throwing an IndexOutOfBounds exception with the error message

Index 5 out of bounds for length 5

Either behavior is incorrect. This is a valid profile and snapshot generation should happen.

To Reproduce

1. Using the following dependencies in pom.xml

<dependency>
            <groupId>ca.uhn.hapi.fhir</groupId>
            <artifactId>hapi-fhir-validation</artifactId>
            <version>7.0.2</version>
</dependency>
<dependency>
            <groupId>ca.uhn.hapi.fhir</groupId>
            <artifactId>hapi-fhir-client</artifactId>
            <version>7.0.2</version>
</dependency>
 <dependency>
            <groupId>ca.uhn.hapi.fhir</groupId>
            <artifactId>hapi-fhir-structures-r4</artifactId>
            <version>7.0.2</version>
</dependency>

2. Convert the base StructureDefinition (in file extension.json attached) and current StructureDefinition(sd.json attached - taken from https://simplifier.net/Basisprofil-DE-R4/ExtensionMehrfachcodierungKennzeichen/~json ) into StructureDefinition objects.

extension.json
sd.json

String baseStructureDefinition;
String requestStructureDefinition;
org.hl7.fhir.r4.model.StructureDefinition baseDefinition = (org.hl7.fhir.r4.model.StructureDefinition) r4fhirContext.newJsonParser()
                        .parseResource(baseStructureDefinition);
org.hl7.fhir.r4.model.StructureDefinition requestDefinition = (org.hl7.fhir.r4.model.StructureDefinition) r4fhirContext.newJsonParser()
                .parseResource(requestStructureDefinition);

Use the HAPI snapshot generation APIs.

FhirContext fhirContext = FhirContext.forR4();
ProfileUtilities profileUtils = new ProfileUtilities(
                    new HapiWorkerContext(fhirContext, new DefaultProfileValidationSupport(fhirContext)), new ArrayList<ValidationMessage>(), null);
            profileUtils.generateSnapshot(baseDefinition, requestDefinition, null, null, null);

Expected behavior
Snapshot generation should happen successfully.

Screenshots

Environment (please complete the following information):

• HAPI FHIR Version: 7.0.2 and earlier

Additional notes

Simplifier APIs are able to handle the snapshot generation - https://simplifier.net/Basisprofil-DE-R4/ExtensionMehrfachcodierungKennzeichen/~json