Enum UnmergedFieldAction
What to do with a merge field the data did not supply a value for.
public enum UnmergedFieldActionFields
Keep = 0Leave the field, markup and cached result intact.
RemoveField = 1Remove the field markup but keep its cached result as ordinary text.
RemoveFieldAndText = 2Remove the field and its result entirely.
Remarks
A field whose value is null or empty is not the same as a field whose name the data does not carry. The first is ordinary and merges as empty; the second is almost always a template bug, and is reported through UnmergedFieldNames whatever this setting says.