What relationship does law have to other normative systems, and most importantly, morality?

Critically discuss the following claim:

'Law is necessarily moral. It becomes moral any time content is injected into otherwise hollow concepts, like reasonableness and the reasonable person. Hence legal positivism is, necessarily, false.'

Further Research Area

• Legal positivism and its opponents
• The autonomy of law
• Legal 'Reasonableness' and its relation to rationality
• Uses of the 'Reasonable Person' construct
• Morality and rationality