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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 get_default(self):
 """Get a string representation of a param's default value. Returns None if there is no default value for this param. """

        definfo = functionutils.DefinitionInfo.read(self._function)
        for arg, default in definfo.args_with_defaults:
            if self.argname == arg:
                return default
        return None