Preview Search displays an empty string if column data is null

[ptitzler]

It appears that if a data value is null, an empty string is displayed in the rows preview. I loaded the movies sample data set and previewed the search. The first 20 rows did not display any data under the rating and earnings_rank headings, giving the appearance that there's a bug. Only after I inspected the raw data I realized that the sample rows shown contained null values. It might be good if a place holder string could be displayed instead of the empty string to avoid confusion.

[ptitzler]