As you did not provide any code snippet I think your query could be like below
SELECT COUNT([uid]) AS [new_count]
FROM [Users]
This above query will produce the warning if any column of the table contains null value. Better to write the query like below
SELECT COUNT(CASE WHEN [uid] IS NULL THEN 0 ELSE 1 END) AS [new_count]
FROM [Users]
Hope this will solve your issue.