update changelog

Author: efrederickson

docs/changelog.rst

@@ -24,6 +24,7 @@ Development
 - BugFix - Calling .clear on a ListField wasn't being marked as changed (and flushed to db upon .save()) #2858
 - Improve error message in case a document assigned to a ReferenceField wasn't saved yet #1955
 - BugFix - Take `where()` into account when using `.modify()`, as in MyDocument.objects().where("this[field] >= this[otherfield]").modify(field='new') #2044
+- fix: exception on null embedded scalar values
 
 Changes in 0.29.0
 =================