User-defined vertex ids - why do they need to end in 000?

[](https://groups.google.com/forum/?hl=En&nomobile=true#!topic/janusgraph-users/xM8jAGLsklQ)

I tried to define a user-id but I have encountered the same issue as above, which i have to supply id that ends in 000.

And on line 507 of StandardJanusGraphTx, we have this pre-condition:
`Preconditions.checkArgument(vertexId == null || IDManager.VertexIDType.NormalVertex.is(vertexId), "Not a valid vertex id: %s", vertexId);`

What's the reason for this constraint? And could this be a bug? Should the pre-condition be applied to VertexIDType.UserVertex instead?

Start with the linked discussion and the precondition at line 507 of StandardJanusGraphTx, then trace IDManager.VertexIDType.NormalVertex and UserVertex. Determine why user-defined vertex IDs must end in 000 and whether the precondition accepts the wrong ID type; done means the behavior is explained and any required correction is covered by tests.

Written by the indexing model from the issue text.