code: private static TupleRef asTupleRef( JsonObject json)
      {
      TupleRef tupleRef = new TupleRef();
  
      json.keySet().stream()
        .forEach( var -> {
          try
            {
            tupleRef.addVarBinding( new VarBinding( var, ObjectUtils.toObject( json.getString( var))));
            }
          catch( GeneratorSetException e)
            {
            throw new GeneratorSetException( String.format( "Error adding binding for variable=%s", var), e);
            }
          });
  
      return tupleRef;
      }
docs: Returns the TupleRef represented by the given JSON object.