Cyclic graph Json exception

[petko-boyadzhiev]

If arcadeanalytics supports cyclic graphs then this is a bug. If not, the error should state that fact instead of Json mapping exception.

To Reproduce
Steps to reproduce the behavior:

1. start empty janusgraph
2. start arcadeanalytics
3. Open the gremlin console via "docker exec -it /bin/bash", then "./bin/gramlin.sh"
4. ":remote connect tinkerpop.server conf/remote.yaml session"
5. ":remote console"
6. "GraphOfTheGodsFactory.load(graph)" it should output ==>null
7. Login in arcade and create datasource for this janusgraph.
   Note that you should write something in username and password and then delete it in order for the values to become empty strings.
8. Index the datasource
9. Create graph widget and open it
10. Search with this query ""g.V().has("name","cerberus")
11. Mark the vertex and traverse "battled"
    An error will appear:
    Could not write JSON: Direct self-reference leading to cycle; nested exception is com.fasterxml.jackson.databind.JsonMappingException: Direct self-reference leading to cycle

• OS: Mac OS
• Browser Chrome
• Version: Version 78.0.3904.70 (Official Build) (64-bit)

The visualization for graph of the gods can be found here:
http://s3.thinkaurelius.com/docs/titan/0.5.0/images/graph-of-the-gods.png
Do note that the edges are black and the image is transparent, so view it with white background :)

[arcade-player]

thank you forthe detailed report, we will investigate it