fields property
The fields that should be updated.
At least one field must be specified. The root pageProperties is implied
and should not be specified. A single "*" can be used as short-hand for
listing every field. For example to update the page background solid fill
color, set fields to "pageBackgroundFill.solidFill.color". To reset a
property to its default value, include its field name in the field mask
but leave the field itself unset.
Implementation
core.String? fields;