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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 from_param(cls, param):
 """ Construct a CommandSpec from a parameter to build_scripts, which may be None. """

        if isinstance(param, cls):
            return param
        if isinstance(param, list):
            return cls(param)
        if param is None:
            return cls.from_environment()
        # otherwise, assume it's a string.
        return cls.from_string(param)