code: protected JCExpression checkExprStat(JCExpression t) {
          if (!TreeInfo.isExpressionStatement(t)) {
              JCExpression ret = F.at(t.pos).Erroneous(List.<JCTree>of(t));
              error(ret, "not.stmt");
              return ret;
          } else {
              return t;
          }
      }
docs: Check that given tree is a legal expression statement.