def _ref_exists(self):
        self._collect_soft_chain()

        found_ref = False
        for node in self.nodes:
            if node.id == self.ref:
                self.file = os.path.join(Constants.ALTER_DIR, node.filename)
                found_ref = True
                break

        return found_ref
Check that the references (self.ref) exists within the build-chain. And, if so,
dataset/ETHPy150Open appnexus/schema-tool/schematool/command/resolve.py/ResolveCommand._ref_exists