Generated value must be null or string

[0x346e3730]

Hello,

When using the anonymizer with the bundle, I encountered this error.
It comes from WebnetFr\DatabaseAnonymizer\Anonymizer line 53.

I don't understand why there is this constraint :

if (null !== $anonValue && !\is_string($anonValue)) {
    throw new InvalidAnonymousValueException('Generated value must be null or string');
}

I had this error when using numbers : why would numbers be forbidden/invalid ? I can't think of a use case.

Thank's.