document empty facets

Fil · Fil · commit 40df15b52d3e · 2021-08-20T17:27:03.000+02:00
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -126,7 +126,7 @@ Plot.plot({
 })
 ```
 
-When the facet *data* is null, a better error message is thrown.
+Empty facets —which can happen when faceting over two dimensions— are now left blank. When the facet *data* is null, a better error message is thrown.
 
 ### Transforms
 
