Arne Jørgensen 65b78f7ffe Handle empty date-time gracefully
Some API's return an invalid, empty string as a date-time property.

DateTime::__construct() will return the current time for empty input
which is probably not what is meant.

The invalid empty string is probably to be interpreted as a missing
field/value.

Let's handle this graceful.
2016-03-15 06:46:51 +01:00
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2016-03-15 06:46:51 +01:00
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