Allow Observation BMI resource with dataAbsentReason (FI-3752)

[yunwwang]

This is reported in slack thread here.

When server send an Observation BMI resource with dataAbsentReason, validator throw a validation error:

Observation: Slice 'Observation.value[x]:valueQuantity': a matching slice is required, but not found (from http://hl7.org/fhir/StructureDefinition/bmi|4.0.1).

The reason is that all resources have to be valid no only to its declared profiles but also to corresponding FHIR resource type and FHIR core profiles. When validator validates a US Core BMI observation resource, it validates it using both US Core BMI profile and FHIR BMI profile.

US Core BMI profile inherits from FHIR vital-signs profile which allows the choice between value[x] and dataAbsentReason. FHIR BMI profile also inherits from FHIR vital-signs profiles but restricts the choice to mnadate value[x] to be presented.

This combination causes the validation error you have seen.

Inferno will add an filter for this error message in the next release. At the same time, if you want to continue the testing, the only work around is to remove any BMI (and similar Observation vital signs ) resources which having dataAbsentReason only from server responses.