Hi Ptrick,
Thanks for your interest in Syncfusion components.
The provided query will return the data only for non-null inputs, you can use the OR SQL Logical operator to return data for null type values inputs as shown in the below query.
SQL query:
select distinct Partnum from Artikel where PARTNUM like '%' + @SearchArticle + '%' OR ( (@SearchArticle is NUll) AND (PARTNUM is NULL) )
Regards,
Vijay R.