EXEC_BAD_ACCESS when encoding dates

[firefightingcode]

When encoding Date objects, it crashes with a EXEC_BAD_ACESS in
fileprivate func box_<T : Encodable>(_ value: T) throws -> NSObject? {
(DictionaryEncoder.swift, line 810).

It's reproducable with the delivered unit tests:
testEncodingDateFormats()

Xcode 10.1
Swift 4
Deployment target 11.0