fix: export_pdf failed without metadata #565

Job	Run time
Collect changes / collect-changes	6s
Python tests / types-check	1m 3s
Python tests / unit-tests (py313)	2m 56s
Python tests / lint-and-format-check	45s
Python tests / unit-tests (py312)	6m 1s
Python tests / unit-tests (py311)	2m 14s
Python tests / unit-tests (py310)	2m 11s
Python tests / unit-tests (py39)	2m 29s
status-check	1s
	17m 46s

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