RFR: 8221924: get(null) on single-entry unmodifiable Map returns null instead of throwing NPE

Stuart Marks stuart.marks at oracle.com
Thu Apr 4 21:11:57 UTC 2019

Hi all,

An unmodifiable map with one entry doesn't throw NPE from get(null). Instead, it 
returns null. This makes it quite an outlier:

Map.of().get(null) ==> NPE
Map.of().containsKey(null) ==> NPE
Map.of().containsValue(null) ==> NPE

Map.of(1, 2).get(null) ==> returns null  ***
Map.of(1, 2).containsKey(null) ==> NPE
Map.of(1, 2).containsValue(null) ==> NPE

Map.of(1, 2, 3, 4).get(null) ==> NPE
Map.of(1, 2, 3, 4).containsKey(null) ==> NPE
Map.of(1, 2, 3, 4).containsValue(null) ==> NPE

It should be fixed to throw NPE like all the other cases.

This is a tiny incompatible change, so I intend to file a CSR. Tier1, 2, and 3 
tests all pass though.

I think this change should also be backported to 11. We're fairly early in the 
11 LTS lifetime, so it'd be good to fix this now.







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