Function maskChineseIdCard

maskChineseIdCard(text?: string | null): string | undefined
Returns a masked Chinese ID card number, which keeps the first 3 and last 4 characters

Note that only the format is verified, the checksum character is not validated here, so that malformed data stored in the database can still be masked
Parameters
- Optionaltext: string | null
  The text to mask
Returns string | undefined
a masked Chinese ID card number, or undefined if the given text is invalid
Author
David Hsing
Example
```
maskChineseIdCard(undefined);    // undefined
maskChineseIdCard('11010519491231002X');    // '110***********002X'
maskChineseIdCard('11010519491231');    // undefined
```