Convert all content types to string #797

Job	Run time
unit-tests (ubuntu-latest, v0.11.1)	1m 2s
unit-tests (macos-latest, nightly)	48s
unit-tests (ubuntu-latest, nightly)	31s
unit-tests (macos-latest, v0.11.1)	46s
unit-tests (windows-latest, v0.11.1)	52s
unit-tests (windows-latest, nightly)	59s
	4m 58s

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