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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def rename_key(self, old_key, new_key):
 """Rename a reference that may or may not exist. Only handles the reference itself, so this is the other half of what `rename` does. If old_key is not in referenced_by, this is a no-op. :param _ReferenceKey old_key: The old key to be renamed. :param _ReferenceKey new_key: The new key to rename to. :raises InternalError: If the new key already exists. """

        if new_key in self.referenced_by:
            dbt.exceptions.raise_cache_inconsistent(
                'in rename of "{}" -> "{}", new name is in the cache already'
                .format(old_key, new_key)
            )

        if old_key not in self.referenced_by:
            return
        value = self.referenced_by.pop(old_key)
        self.referenced_by[new_key] = value