[An error message in pick_type](https://github.com/ResearchObject/ro-crate-py/blob/1a45d86711ad67e1b8751c98e2341c20fde091dd/rocrate/rocrate.py#L55) assumes that the entity has an `@id`, but [we pop it before calling the function](https://github.com/ResearchObject/ro-crate-py/blob/1a45d86711ad67e1b8751c98e2341c20fde091dd/rocrate/rocrate.py#L158). If possible, we should probably change callers so they don't pop anything, rather than fix `pick_type`.
An error message in pick_type assumes that the entity has an
@id, but we pop it before calling the function. If possible, we should probably change callers so they don't pop anything, rather than fixpick_type.