I want to add a vertex to JanusGraph by GremlinPython, and I already set graph.set-vertex-id=true in config, but I always get error:GremlinServerError: 500: Not a valid vertex id: 5678
I want to set a custom id to vertex, I only know the id should be a long type, some id set success, like:2048, 123456...; But more id set failed, it raise a error: GremlinServerError: 500: Not a valid vertex id: 5678. 
My add vertex code is:
vip = g.addV().property(T.id, 5678).property("name", "domain").property("value", "www.google.com").next()

Please tell me what is a valid id?
The type is Long, but you need to send it in a string.

vip = g.addV().property(T.id, '5678').property("name", "domain").....
gremlin-python: what is a valid vertex custom id?