message: fix Statement::toJson() sub_statements assert
diff: @@ -158,7 +158,7 @@ PyObject * Statement::toJson() const {
  return exprs[0]->toJson();
  } else if (type == s_IF) {
  PyDict_SetItemString(d, "cond", exprs[0]->toJson());
  - assert(sub_statements);
  + assert(sub_statements.size());
  addJsonArrP(d, "ifTrue", *sub_statements[0]);
  PyObject * elseIfs;
  size_t elif_cnt;
  