How to Serialize ARQ Algebra as ASK/CONSTRUCT SPARQL Query?

Question

My intention is to

1. Parse a SPARQL query to the ARQ Algebra.
2. Get some work done.
3. Parse the ARQ Algebra back to SPARQL query.

Approach below seems to work as expected for SELECT queries, but fails for ASK and CONSTRUCT queries. I will highly value your help on this one. :)

Op opRoot = Algebra.compile(QueryFactory.create(sparqlQueryStr));

OpWalker.walk(opRoot, visitor);

OpAsQuery.asQuery(opRoot).serialize();