Use lowercase true, false and null constants

apps/dav/lib/Connector/Sabre/AnonymousOptionsPlugin.php

apps/dav/lib/Connector/Sabre/FilesPlugin.php

build/integration/features/bootstrap/Sharing.php

lib/private/Contacts/ContactsMenu/ContactsStore.php

lib/private/Files/Cache/Wrapper/CacheJail.php

lib/private/Template/JSCombiner.php

lib/private/legacy/util.php

lib/public/Util.php

tests/lib/Avatar/UserAvatarTest.php

tests/lib/DB/LegacyDBTest.php

tests/lib/Files/Stream/EncryptionTest.php

tests/lib/Mail/MessageTest.php

tests/lib/TagsTest.php