<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def preprocess_gold(self, docs_golds):
 """Can be called before training to pre-process gold data. By default, it handles nonprojectivity and adds missing tags to the tag map. docs_golds (iterable):
 Tuples of `Doc` and `GoldParse` objects. YIELDS (tuple):
 Tuples of preprocessed `Doc` and `GoldParse` objects. """

        for name, proc in self.pipeline:
            if hasattr(proc, "preprocess_gold"):
                docs_golds = proc.preprocess_gold(docs_golds)
        for doc, gold in docs_golds:
            yield doc, gold