Set default value for empty stringSlice to [] in docs #1664

Job	Run time
build-base-image	10m 28s
make-date-tag	1s
build-server-images (cache)	4m 12s
build-server-images (origin)	4m 13s
build-server-images (director)	4m 21s
build-server-images (registry)	4m 36s
build-server-images (osdf-cache)	4m 8s
build-server-images (osdf-origin)	4m 18s
build-server-images (osdf-director)	4m 14s
build-server-images (osdf-registry)	4m 32s
	45m 3s

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