[BUG] Undefined array key 3 warning when using date interval in JSON-LD

[seth-shaw-asu]

What steps does it take to reproduce the issue?

Create an item with and EDTF interval, e.g. '2022/2023', and view the JSON-LD. This creates a warning in the logs stating "Undefined array key 3" because the converter is expecting a single date.

What did you expect to happen?

No warnings. It should return the earliest ISO 8601 date value for the interval.