Internally, we've been using an expiration of 0 to mean "never expires".
For LN invoices, BOLT-11 does not specify what an expiration of 0 means.
Other clients seem to treat it as "0 seconds" (i.e. already expired).
This means there is no way to create a BOLT-11 invoice that "never" expires.
For LN invoices,
- we now treat an expiration of 0, , as "0 seconds",
- when creating an invoice, if the user selected never, we will put 100 years as expiration
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