SnapshotGenerator: Keep snapshot when differential is missing

[mharthoorn]

Problem: If the snapshot generator encounters a StructureDefinition (of type LogicalModel) that already has a snapshot, but not a differential, it will remove that snapshot without replacing it (only when SnapshotGeneratorSettings.ForceRegenerateSnapshots is set to true)

Solution The SnapshotGenerator should not remove a snapshot when there is no differential present in a StructureDefinition.

Alternatives

• Create an extra setting SnapshotGeneratorSettings.SkipRegenerateOnMissingDifferential
• Throw an Exception
• Add a warning to the OperationOutcome

Additional context In bulk snapshot operations this situation tends to go unnoticed and leads to loss of data / correctness in publications.