code: public static String[] replaceEqualNullWithIsNull(String fieldName, String... sqlFragments) {
          String namedParam = "{" + fieldName + "}";
          for (int i = 0; i < sqlFragments.length; i++) {
              String fragment = sqlFragments[i];
              String equalNull = findEqualNamedParamPattern(fragment, namedParam);
              while (equalNull != null) {
                  fragment = fragment.replaceAll(equalNull, " is null");//注意这里is null 前面的空格，很重要
                  sqlFragments[i] = fragment;
                  equalNull = findEqualNamedParamPattern(fragment, namedParam);
              }
          }
          return sqlFragments;
      }
docs: 将形如 xxx = {fieldName} 的语句全部转为 xxx is null
  注意，该算法修改了数组参数sqlFragments内的数组元素