presto-main/src/main/java/io/prestosql/sql/planner/plan/IndexJoinNode.java/IndexJoinNode/EquiJoinClause
class IndexJoinNode:        @JsonCreator
        public EquiJoinClause(@JsonProperty("probe") Symbol probe, @JsonProperty("index") Symbol index)
        {
            this.probe = requireNonNull(probe, "probe is null");
            this.index = requireNonNull(index, "index is null");
        }