Inspect flat file contents prior to data copy

I am using Data Flows to import data from CSV files into DataVerse. That works fine. I have Datasets defined already. I need to inspect the contents of the file prior to loading it. I need to make sure that one column is not NULL. If there is a NULL or missing value in that column, do not run the Data Flow.

I was thinking of doing a ROW COUNT of the CSV file WHERE the column in question is NULL. From there, if that task output value is anything other than 0, I can branch off in an IF task.

What task, or combination of tasks could help me do this ROW COUNT with a WHERE clause?

Thanks in advance.