Return string with each value separated or null if all are null, using FOR XML PATH

Question

I have a query like this:

select stuff (
        (select '; ' + isnull(org.Number, '-')
        from Organization org
        for xml path('')), 1, 2, ''
       )

I need to return a string with all values, including nulls, so that its amount of values is equal to amount of organizations, but if ALL values are empty or null, I need to return empty string or null (doesn't matter).

First thought was to use regex and check if there are digits in returned query. but it's not so easy to use. Is there some other options to solve it?

For example, if table Organization contains

ID | Number
1  | 123456
2  | null
3  | 3232

then resulted string has to be '123456; -; 3232'

if table Organization contains

ID | Number
1  | null
2  | null
3  | null

resulted string has to be null

Answer 1

Here's one way

select
    iif(patindex('%[0-9]%', res) = 0, null, res)
from
    (select res = stuff((
        select
            '; ' + isnull(cast(number as varchar(200)), '-')
        from 
            Organization
        order by id
        for xml path('')
    ), 1, 2, '')
) t