added test cases for flags with empty string value #218

Job	Run time
test-node-server-sdk / lint-test-sdk (18)	48s
test-android-sdk / Test API Level 26	4m 27s
test-java-sdk / lint-test-sdk (8)	36s
test-node-server-sdk / lint-test-sdk (20)	51s
test-java-sdk / lint-test-sdk (11)	35s
test-node-server-sdk / typecheck (18)	46s
test-android-sdk / Test API Level 31	4m 33s
test-node-server-sdk / lint-test-sdk (22)	46s
test-java-sdk / lint-test-sdk (17)	32s
test-android-sdk / Test API Level 34	5m 5s
test-node-server-sdk / typecheck (20)	43s
test-node-server-sdk / lint-test-sdk (23)	42s
test-node-server-sdk / typecheck (22)	42s
test-java-sdk / lint-test-sdk (21)	40s
test-node-server-sdk / typecheck (23)	48s
test-react-native-sdk / build	21s
test-react-native-sdk / lint	26s
test-react-native-sdk / test	25s
test-dotnet-sdk / build-and-run-tests	27s
test-golang-sdk / test-sdk	32s
test-ios-sdk / build	33s
test-java-common-sdk / lint-test-sdk (8)	54s
test-java-common-sdk / lint-test-sdk (11)	53s
test-js-client-sdk / lint-test-sdk (18)	46s
test-java-common-sdk / lint-test-sdk (17)	51s
test-java-common-sdk / lint-test-sdk (21)	55s
test-js-client-sdk / lint-test-sdk (20)	37s
test-js-client-sdk / lint-test-sdk (22)	45s
test-js-client-sdk / typecheck (18)	37s
test-js-client-sdk / lint-test-sdk (23)	42s
test-js-client-sdk / typecheck (20)	42s
test-js-client-sdk / typecheck (22)	36s
test-multiplatform-sdk / Cargo Build & Test (stable)	2m 21s
test-js-client-sdk / typecheck (23)	37s
test-php-sdk / build-and-test	9s
	36m 43s

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