csv output collapses empty columns

If I query some metric that does not have data for each of the UUIDs, then empty columns are not retained, and the data always shifts left.

This makes it difficult to determine which UUIDs are missing data.

Request: Empty columns should be preserved in the rendered output.

Start by locating the CSV rendering entry point used when metric data is missing for some UUIDs, then trace how rows and columns are assembled. Confirm that missing values retain their UUID positions instead of shifting later values left, and verify the rendered output with a case containing empty columns.

Written by the indexing model from the issue text.