Convert all content types to string #848

Job	Run time
unit-tests (macos-latest, v0.11.2)	53s
unit-tests (ubuntu-latest, v0.11.2)	28s
unit-tests (ubuntu-latest, nightly)	34s
unit-tests (macos-latest, nightly)	48s
unit-tests (windows-latest, nightly)	1m 7s
unit-tests (windows-latest, v0.11.2)	1m 5s
	4m 55s

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