cypher-for-gremlin: Question: translation result cannot run on Janus Graph

First thanks for your contributions for this useful tool.

I translated cypher with parameters to gremlin script using this tool.

Cypher: MATCH (arch:Architecture{_id: {archId}}) RETURN arch AS arch

Translated gremlin script: g.V().as('arch').hasLabel('Architecture').where(__.choose(__.constant(archId), __.constant(archId), __.constant(' cypher.null')).is(neq(' cypher.null')).as(' GENERATED1').select('arch').values('_id').where(eq(' GENERATED1'))).select('arch').project('arch').by(__.choose(neq(' cypher.null'), __.valueMap(true)))

This gremlin script can run successfully on Neo4j. But after I switched db to JanusGraph, I cannot get result and got this error.

I commit the gremlin script using following code in JavaScript. client.submit(gremlinScript, params)

And I also created index for _id property.

Could anyone help with this issue? And what is the best practice for this kind of requirements?