Paragraphs submodule assumes parent exists

Problem/Motivation

Attempting to delete a paragraph which no longer has a parent, for example using the batch cleanup provided by entity_reference_revisions module, leads to an error about calling getEntityType() on null in ParagraphPersistance::purge().

Steps to reproduce

Easiest way is to programmatically create a paragraph without a parent, save it, then try to delete it while the module is active.

Proposed resolution

Check if the parent exists before attempting to

Remaining tasks

None

User interface changes

None

API changes

None

Data model changes

None