Make map.get work with null key

[addshore]

I appear to be able to set a null key in a map, however I can't use .get to retrieve it

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Class 'Null_' does not have any method 'hash-code'.
  0: HashedInsertionOrderedCollection_.hash-code_ <sdk>/core/collections.toit:2188:16
  1: HashedInsertionOrderedCollection_.find_ <sdk>/core/collections.toit:2303:13
  2: Map.[]=                   <sdk>/core/collections.toit:2858:15
  3: Header.STATUS-MAP         <pkg:lightbug>/protocol/Header.toit:32:11

As I can set a bull key, I'd expect to be able to .get it