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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 dump_file_by_path(self, path, **kwargs):
 """ Returns the concrete content for a file by path. :param path: file path as string :param kwargs: passed to state.solver.eval :return: file contents as string """

        file = self.state.fs.get(path)
        if file is None:
            return None
        return file.concretize(**kwargs)