Return empty string when date is null #1667

Job	Run time
Run Coverity tests	0s
Run CodeQL tests	3m 56s
Build on macOS for macos	2m 39s
Build on Fedora 40	1m 3s
Build on macOS for iphoneos	58s
Deploy pages	0s
Build on Fedora 41	1m 8s
Build on macOS for iphonesimulator	1m 5s
Build on Ubuntu 20.04	2m 56s
Build on Fedora rawhide	59s
Build on Ubuntu 22.04	2m 39s
Build on Ubuntu 24.04	2m 47s
Build on Windows (143, x86)	6m 44s
Build on Ubuntu 24.10	2m 33s
Build on macOS for androidarm	58s
Build on Windows (143, x64)	6m 48s
Build on macOS for androidarm64	1m 5s
Build on Windows (143, arm64)	6m 15s
Build on macOS for androidx86_64	1m 15s
Build on Windows (142, x86)	6m 20s
Build on Windows (142, x64)	7m 15s
Build on Windows (142, arm64)	5m 54s
	1h 5m 17s

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