Resource Indexer Exception in causes observations sync download to fail.

[aditya-07]

Describe the bug
Resource Indexer has issue extracting Temperature QuantityValue in the following Observation taken from the Synthea dataset.

{
	"resourceType": "Observation",
	"id": "1595",
	"meta": {
		"versionId": "1",
		"lastUpdated": "2021-10-21T08:29:32.481+00:00",
		"source": "#RqWIwZVJSul7Y3tp"
	},
	"status": "final",
	"category": [{
		"coding": [{
			"system": "http://terminology.hl7.org/CodeSystem/observation-category",
			"code": "vital-signs",
			"display": "vital-signs"
		}]
	}],
	"code": {
		"coding": [{
			"system": "http://loinc.org",
			"code": "8331-1",
			"display": "Oral temperature"
		}],
		"text": "Oral temperature"
	},
	"subject": {
		"reference": "Patient/1561"
	},
	"encounter": {
		"reference": "Encounter/1593"
	},
	"effectiveDateTime": "2011-09-15T12:22:44-04:00",
	"issued": "2011-09-15T12:22:44.702-04:00",
	"valueQuantity": {
		"value": 37.65532501487887,
		"unit": "Cel",
		"system": "http://unitsofmeasure.org",
		"code": "Cel"
	}
}

Exception:

10-26 12:21:42.804 20937 20978 W System.err: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String org.fhir.ucum.Decimal.asDecimal()' on a null object reference
10-26 12:21:42.805 20937 20978 W System.err: 	at com.google.android.fhir.UnitConverter.getCanonicalForm$engine_debug(UnitConverter.kt:47)
10-26 12:21:42.805 20937 20978 W System.err: 	at com.google.android.fhir.index.ResourceIndexer.quantityIndex(ResourceIndexer.kt:307)
10-26 12:21:42.805 20937 20978 W System.err: 	at com.google.android.fhir.index.ResourceIndexer.extractIndexValues(ResourceIndexer.kt:96)
10-26 12:21:42.805 20937 20978 W System.err: 	at com.google.android.fhir.index.ResourceIndexer.index(ResourceIndexer.kt:68)
10-26 12:21:42.805 20937 20978 W System.err: 	at com.google.android.fhir.db.impl.dao.ResourceDao.insertResource(ResourceDao.kt:202)
10-26 12:21:42.805 20937 20978 W System.err: 	at com.google.android.fhir.db.impl.dao.ResourceDao.insertAll$suspendImpl(ResourceDao.kt:74)
10-26 12:21:42.805 20937 20978 W System.err: 	at com.google.android.fhir.db.impl.dao.ResourceDao.insertAll(Unknown Source:4)
10-26 12:21:42.805 20937 20978 W System.err: 	at com.google.android.fhir.db.impl.DatabaseImpl.insertRemote(DatabaseImpl.kt:68)
10-26 12:21:42.805 20937 20978 W System.err: 	at com.google.android.fhir.db.impl.DatabaseImpl$insertSyncedResources$2.invokeSuspend(DatabaseImpl.kt:97)
10-26 12:21:42.805 20937 20978 W System.err: 	at com.google.android.fhir.db.impl.DatabaseImpl$insertSyncedResources$2.invoke(Unknown Source:12)
10-26 12:21:42.805 20937 20978 W System.err: 	at com.google.android.fhir.db.impl.DatabaseImpl$insertSyncedResources$2.invoke(Unknown Source:7)
10-26 12:21:42.805 20937 20978 W System.err: 	at androidx.room.RoomDatabaseKt$withTransaction$2.invokeSuspend(RoomDatabase.kt:58)
10-26 12:21:42.805 20937 20978 W System.err: 	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
10-26 12:21:42.805 20937 20978 W System.err: 	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
10-26 12:21:42.805 20937 20978 W System.err: 	at kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.common.kt:274)
10-26 12:21:42.805 20937 20978 W System.err: 	at kotlinx.coroutines.BlockingCoroutine.joinBlocking(Builders.kt:85)
10-26 12:21:42.805 20937 20978 W System.err: 	at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking(Builders.kt:59)
10-26 12:21:42.806 20937 20978 W System.err: 	at kotlinx.coroutines.BuildersKt.runBlocking(Unknown Source:1)
10-26 12:21:42.806 20937 20978 W System.err: 	at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking$default(Builders.kt:38)
10-26 12:21:42.806 20937 20978 W System.err: 	at kotlinx.coroutines.BuildersKt.runBlocking$default(Unknown Source:1)
10-26 12:21:42.806 20937 20978 W System.err: 	at androidx.room.RoomDatabaseKt$acquireTransactionThread$$inlined$suspendCancellableCoroutine$lambda$2.run(RoomDatabase.kt:121)
10-26 12:21:42.806 20937 20978 W System.err: 	at androidx.room.TransactionExecutor$1.run(TransactionExecutor.java:47)
10-26 12:21:42.806 20937 20978 W System.err: 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
10-26 12:21:42.806 20937 20978 W System.err: 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
10-26 12:21:42.806 20937 20978 W System.err: 	at java.lang.Thread.run(Thread.java:923)
10-26 12:21:42.809 20937 20972 D FhirSynchronizer: download ended at 1635231102809, Tue Oct 26 12:21:42 GMT+05:30 2021, total time 11397 ms

[epicadk]

FHIR/Ucum-java#26