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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 _build_xrefs(self):
        '''
        Internal function to populate the xrefs list with the external
        references to be used in searching plugins and potentially
        other functions as well.
        '''
        xrefs = set()

        plugins = self.plugins()
        for plugin in plugins:
            for xref in plugin['xrefs'].split(', '):
                xrf = xref.replace('-', '_').split(':')[0]
                if xrf is not '':
                    xrefs.add(xrf)
        self._xrefs = list(xrefs)