[Issue 22572] Cannot define SumType over immutable struct with Nullable

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=22572

--- Comment #2 from Paul Backus <snarwin+bugzilla at gmail.com> ---
Fixed in sumtype v1.2.1 on code.dlang.org by this PR:

https://github.com/pbackus/sumtype/pull/78

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