mirror property
Mirror names why the columnar copy did not take this batch, when it did not. The record is already durable in the tenant's own store by then — the warehouse copy exists to make a training join cheap, and its absence is a gap in that join, never a lost label.
Please note: This property should have been non-nullable! Since the specification file does not include a default value (using the "default:" property), however, the generated source code must fall back to having a nullable type. Consider adding a "default:" property in the specification file to hide this note.
Implementation
String? mirror;