presto-main/src/main/java/io/prestosql/sql/planner/iterative/rule/PushProjectionThroughUnion.java/PushProjectionThroughUnion/nonTrivialProjection
class PushProjectionThroughUnion:    private static boolean nonTrivialProjection(ProjectNode project)
    {
        return !project.getAssignments()
                .getExpressions().stream()
                .allMatch(SymbolReference.class::isInstance);
    }