presto-main/src/main/java/io/prestosql/sql/planner/RelationPlanner.java/RelationPlanner/processAndCoerceIfNecessary
class RelationPlanner:    private RelationPlan processAndCoerceIfNecessary(Relation node, Void context)
    {
        Type[] coerceToTypes = analysis.getRelationCoercion(node);

        RelationPlan plan = this.process(node, context);

        if (coerceToTypes == null) {
            return plan;
        }

        return addCoercions(plan, coerceToTypes);
    }