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Longer take:
Defining what is morally right requires value judgement, and Nihilism rejects morality. What Is (facts) can't tell us what we ought to do. [1]
To build a moral framework on what one ought to do, you must necessarily ascribe meaning and value judgement otherwise it can't claim to be moral and it would merely be actions you perform devoid of meaning.
[1] https://en.m.wikipedia.org/wiki/Is%E2%80%93ought_problem