Fatal error when cloning entity with empty paragraphs field of cardinality 1

Using field_info_field is the proper way to do it, since the only indicator should be the cardinality, not the actual value returned. Also, field_info_field() uses static caching and thus is a cheap operation.

Steps to reproduce:

1. Enable translation.
2. Create a node type and enable translation for it.
3. Add a paragraphs field with cardinality 1.
4. Create a new node, leave the field empty.
5. Create a new translation for that node.

In your steps I miss the part where we replicate the content? I just tried adding a translation without replicating and replicating a node and changing the language after that. Still having problems reproducing it.

I forgot to mention that you need to enable paragraphs_i18n as well (bundled with paragraphs). If enabled, the items will be replicated in hook_node_prepare when loading the node form for the new (unsaved translation). The issue should also be reproducable by simply replicating a node via replicate_ui. All you need is a paragraphs field with a cardinality of one, and no items in it. Before that patch this would result in array(null), which would cause a fatal error in the clone statement right at the top of replicate_clone_entity().

The paragraphs_field_property_get() can only return NULL when the cardinality == 1 and the cardinality is already checked there, so it feels unnessecary to check for this again? I do understand performance is not really an issue.

The point is to not make assumptions about the returned values and instead use the information available for that field. It's all about DX. In the end though it is your decision.
By the way, an even safer way to handle this would be to do array_filter($old_items) before iterating over them or instanceof checks in the foreach. That way even array(null) wouldn't matter, and as an added bonus FALSE would also be handled (if for some reason the referenced entity would be missing).

Does the new dev version fix your issue?

I can't test it right now, but looking at the change I'm certain that it fixes the issue.