message: return null P/R in case of a DG space
diff: @@ -935,6 +935,12 @@ void FiniteElementSpace::BuildConformingInterpolation() const
  if (cP_is_set) { return; }
  cP_is_set = true;
  + if (FEColl()->GetContType() == FiniteElementCollection::DISCONTINUOUS)
  + {
  + cP = cR = cR_hp = NULL; // will be treated as identities
  + return;
  + }
  +
  Array<int> master_dofs, slave_dofs, highest_dofs;
  IsoparametricTransformation T;
  