protected Object readValue() {
            skipWhitespace();

            if (isDigitFirst(ch)) {
                return readLongValue();
            }

            if (ch == '"' || ch == '\'') {
                return readString();
            }

            if (ch == 'n') {
                String name = readName();

                if ("null".equals(name)) {
                    return null;
                } else {
                    throw new JSONPathException(path);
                }
            }

            throw new UnsupportedOperationException();
        }
@since 1.2.51
@param json
@param path
@return
src/main/java/com/alibaba/fastjson/JSONPath.java