[BUG Gaia-IR] The plan of pattern matching faces a multi-join error

[longbinlai]

A pattern matching task has been compiled into a plan that involves multi-branch join, which causes "Unsupported" error in the runtime. As an example, a pattern looks as follows

or in the words of Gremlin:

g.V().hasLabel('Cert').match(
    __.as('a').in('r_cert').as('b'),
    __.as('a').out('r_dns_a').as('c'),
    __.as('a').out('r_dns_a').as('d'),
    __.as('b').out('r_dns_a').as('d'),
    __.as('d').out('r_dns_a').as('c')
)

An error message prompts as: