NPE in VPackSerializers when serializing ArangoSearch properties

[wajda]

Problem

NullPointerException is thrown when serializing StoredValue with no compression specified:

Exception in thread "main" com.arangodb.ArangoDBException: com.arangodb.velocypack.exception.VPackParserException: java.lang.NullPointerException
	at com.arangodb.internal.util.ArangoSerializerImpl.serialize(ArangoSerializerImpl.java:82)
	at com.arangodb.internal.util.ArangoSerializerImpl.serialize(ArangoSerializerImpl.java:51)
	at com.arangodb.internal.util.DefaultArangoSerialization.serialize(DefaultArangoSerialization.java:47)
	at com.arangodb.internal.InternalArangoDatabase.createArangoSearchRequest(InternalArangoDatabase.java:470)
	at com.arangodb.async.internal.ArangoDatabaseAsyncImpl.createArangoSearch(ArangoDatabaseAsyncImpl.java:460)
	at za.co.absa.spline.persistence.ArangoManagerImpl.$anonfun$createSearchViews$1(ArangoManager.scala:255)
	at scala.concurrent.Future$.$anonfun$traverse$1(Future.scala:850)
	at scala.collection.TraversableOnce$folder$1.apply(TraversableOnce.scala:196)
	at scala.collection.TraversableOnce$folder$1.apply(TraversableOnce.scala:194)
	at scala.collection.immutable.Set$Set2.foreach(Set.scala:181)
	at scala.collection.TraversableOnce.foldLeft(TraversableOnce.scala:199)
	at scala.collection.TraversableOnce.foldLeft$(TraversableOnce.scala:192)
	at scala.collection.AbstractTraversable.foldLeft(Traversable.scala:108)
	at scala.concurrent.Future$.traverse(Future.scala:850)
	at za.co.absa.spline.persistence.ArangoManagerImpl.createSearchViews(ArangoManager.scala:253)
	at za.co.absa.spline.persistence.ArangoManagerImpl.$anonfun$initialize$9(ArangoManager.scala:77)
	at scala.concurrent.Future.$anonfun$flatMap$1(Future.scala:307)
	at scala.concurrent.impl.Promise.$anonfun$transformWith$1(Promise.scala:41)
	at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:64)
	at java.base/java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1426)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1020)
	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)
	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)
	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)
Caused by: com.arangodb.velocypack.exception.VPackParserException: java.lang.NullPointerException
	at com.arangodb.velocypack.VPack.serialize(VPack.java:860)
	at com.arangodb.velocypack.VPack.serialize(VPack.java:847)
	at com.arangodb.internal.util.ArangoSerializerImpl.serialize(ArangoSerializerImpl.java:77)
	... 24 more
Caused by: java.lang.NullPointerException
	at com.arangodb.internal.velocypack.VPackSerializers.lambda$static$13(VPackSerializers.java:237)
	at com.arangodb.velocypack.VPack.addValue(VPack.java:930)
	at com.arangodb.velocypack.VPack.serializeField(VPack.java:912)
	at com.arangodb.velocypack.VPack.serializeFields(VPack.java:890)
	at com.arangodb.velocypack.VPack.serializeObject(VPack.java:878)
	at com.arangodb.velocypack.VPack.addValue(VPack.java:964)
	at com.arangodb.velocypack.VPack.serialize(VPack.java:858)
	... 26 more

Test case

VPackSerializers.ARANGO_SEARCH_PROPERTIES.serialize(
    new VPackBuilder(),
    "foo",
    new ArangoSearchProperties() {{
        addStoredValues(new StoredValue(List.of("bar")));
    }},
    (builder, attribute, entity) -> {
    }
);