docs: public void compileNode(DecisionService ds, DMNCompilerImpl compiler, DMNModelImpl model) {
          DMNType type = null;
          if (ds.getVariable() == null) { // even for the v1.1 backport, variable creation is taken care in DMNCompiler.
              DMNCompilerHelper.reportMissingVariable(model, ds, ds, Msg.MISSING_VARIABLE_FOR_DS);
              return;
          }
          DMNCompilerHelper.checkVariableName(model, ds, ds.getName());
          if (ds.getVariable() != null && ds.getVariable().getTypeRef() != null) {
              type = compiler.resolveTypeRef(model, ds, ds.getVariable(), ds.getVariable().getTypeRef());
          } else {
              // for now the call bellow will return type UNKNOWN
              type = compiler.resolveTypeRef(model, ds, ds, null);
          }
          DecisionServiceNodeImpl bkmn = new DecisionServiceNodeImpl(ds, type);
          model.addDecisionService(bkmn);
      }