code: public T visitTernaryExpression(TernaryExpression elm, C context) {
          for (Expression element : elm.getOperand()) {
              visitElement(element, context);
          }
          return null;
      }
docs: Visit a TernaryExpression. This method will be called for
  every node in the tree that is a TernaryExpression.
  
  @param elm     the ELM tree
  @param context the context passed to the visitor
  @return the visitor result