<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def update_distant_reference(self, ref):
 """Validate and update the reference in Zotero. Existing fields not present will be left unmodified. """

        self.validate_reference_data(ref["data"])
        self._zotero_lib.update_item(ref)