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