Serialization error querying for vertex properties using GraphBinary

I'm new to using JanusGraph, so apologies if this is caused by something I've done wrong.

The following code in Gremlin.Net produces the following error in JanusGraph.

```csharp
g.AddV("person").Property(Cardinality.Single, "name", "jorge").Iterate();
var result = g.V().Has("person", "name", "jorge").Properties().ToList();
```
```
793973 [gremlin-server-session-1] WARN org.apache.tinkerpop.gremlin.server.op.AbstractEvalOpProcessor - The result [[vp[name->jorge]]] in the request ffcf64e5-6dac-4f8e-a1e6-e4c0c53f1b19 could not be serialized and returned.
java.lang.IllegalStateException
at com.google.common.base.Preconditions.checkState(Preconditions.java:492)
at org.janusgraph.graphdb.relations.RelationIdentifier.getInVertexId(RelationIdentifier.java:63)
at org.janusgraph.graphdb.tinkerpop.io.binary.RelationIdentifierGraphBinarySerializer.writeNonNullableValue(RelationIdentifierGraphBinarySerializer.java:43)
at org.janusgraph.graphdb.tinkerpop.io.binary.RelationIdentifierGraphBinarySerializer.writeNonNullableValue(RelationIdentifierGraphBinarySerializer.java:24)
at org.janusgraph.graphdb.tinkerpop.io.binary.JanusGraphTypeSerializer.writeValue(JanusGraphTypeSerializer.java:89)
at org.janusgraph.graphdb.tinkerpop.io.binary.JanusGraphTypeSerializer.write(JanusGraphTypeSerializer.java:72)
at org.apache.tinkerpop.gremlin.structure.io.binary.GraphBinaryWriter.write(GraphBinaryWriter.java:98)
at org.apache.tinkerpop.gremlin.structure.io.binary.types.VertexPropertySerializer.writeValue(VertexPropertySerializer.java:56)
at org.apache.tinkerpop.gremlin.structure.io.binary.types.VertexPropertySerializer.writeValue(VertexPropertySerializer.java:33)
at org.apache.tinkerpop.gremlin.structure.io.binary.types.SimpleTypeSerializer.writeValue(SimpleTypeSerializer.java:91)
at org.apache.tinkerpop.gremlin.structure.io.binary.types.SimpleTypeSerializer.write(SimpleTypeSerializer.java:73)
at org.apache.tinkerpop.gremlin.structure.io.binary.GraphBinaryWriter.write(GraphBinaryWriter.java:112)
at org.apache.tinkerpop.gremlin.structure.io.binary.types.TraverserSerializer.writeValue(TraverserSerializer.java:49)
at org.apache.tinkerpop.gremlin.structure.io.binary.types.TraverserSerializer.writeValue(TraverserSerializer.java:33)
at org.apache.tinkerpop.gremlin.structure.io.binary.types.SimpleTypeSerializer.writeValue(SimpleTypeSerializer.java:91)
at org.apache.tinkerpop.gremlin.structure.io.binary.types.SimpleTypeSerializer.write(SimpleTypeSerializer.java:73)
at org.apache.tinkerpop.gremlin.structure.io.binary.GraphBinaryWriter.write(GraphBinaryWriter.java:112)
at org.apache.tinkerpop.gremlin.structure.io.binary.types.CollectionSerializer.writeValue(CollectionSerializer.java:52)
at org.apache.tinkerpop.gremlin.structure.io.binary.types.ListSerializer.writeValue(ListSerializer.java:44)
at org.apache.tinkerpop.gremlin.structure.io.binary.types.ListSerializer.writeValue(ListSerializer.java:29)
at org.apache.tinkerpop.gremlin.structure.io.binary.types.SimpleTypeSerializer.writeValue(SimpleTypeSerializer.java:91)
at org.apache.tinkerpop.gremlin.structure.io.binary.types.SimpleTypeSerializer.write(SimpleTypeSerializer.java:73)
at org.apache.tinkerpop.gremlin.structure.io.binary.GraphBinaryWriter.write(GraphBinaryWriter.java:112)
at org.apache.tinkerpop.gremlin.driver.ser.binary.ResponseMessageSerializer.writeValue(ResponseMessageSerializer.java:84)
at org.apache.tinkerpop.gremlin.driver.ser.GraphBinaryMessageSerializerV1.serializeResponseAsBinary(GraphBinaryMessageSerializerV1.java:150)
at org.apache.tinkerpop.gremlin.server.op.AbstractOpProcessor.makeFrame(AbstractOpProcessor.java:286)
at org.apache.tinkerpop.gremlin.server.op.session.SessionOpProcessor.handleIterator(SessionOpProcessor.java:630)
at org.apache.tinkerpop.gremlin.server.op.session.SessionOpProcessor.lambda$iterateBytecodeTraversal$5(SessionOpProcessor.java:421)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:750)
```

Reproduce the Gremlin.Net query with GraphBinary first, then read RelationIdentifier.java and RelationIdentifierGraphBinarySerializer.java at the stack-trace entry points. Trace how JanusGraphTypeSerializer handles the VertexProperty result and verify that the query serializes and returns without IllegalStateException.

Written by the indexing model from the issue text.