added test cases for flags with empty string value #210

Job	Run time
test-dotnet-sdk / build-and-run-tests	36s
test-android-sdk / Test API Level 26	5m 11s
test-ios-sdk / build	39s
test-android-sdk / Test API Level 31	6h 0m 3s
test-golang-sdk / test-sdk	35s
test-java-common-sdk / lint-test-sdk (8)	52s
test-android-sdk / Test API Level 34	5m 45s
test-java-common-sdk / lint-test-sdk (11)	56s
test-java-sdk / lint-test-sdk (8)	33s
test-java-common-sdk / lint-test-sdk (17)	1m 0s
test-js-client-sdk / lint-test-sdk (18)	14s
test-java-sdk / lint-test-sdk (11)	36s
test-js-client-sdk / lint-test-sdk (20)	21s
test-js-client-sdk / typecheck (18)	15s
test-java-common-sdk / lint-test-sdk (21)	59s
test-java-sdk / lint-test-sdk (17)	40s
test-js-client-sdk / lint-test-sdk (22)	15s
test-js-client-sdk / typecheck (20)	18s
test-java-sdk / lint-test-sdk (21)	35s
test-js-client-sdk / typecheck (22)	12s
test-js-client-sdk / lint-test-sdk (23)	15s
test-js-client-sdk / typecheck (23)	14s
test-multiplatform-sdk / Cargo Build & Test (stable)	3m 7s
test-node-server-sdk / lint-test-sdk (18)	1m 4s
test-node-server-sdk / typecheck (18)	50s
test-node-server-sdk / lint-test-sdk (20)	50s
test-php-sdk / build-and-test	2m 24s
test-node-server-sdk / typecheck (20)	44s
test-node-server-sdk / lint-test-sdk (22)	44s
test-node-server-sdk / typecheck (22)	46s
test-node-server-sdk / lint-test-sdk (23)	41s
test-react-native-sdk / build	19s
test-node-server-sdk / typecheck (23)	50s
test-react-native-sdk / lint	19s
test-react-native-sdk / test	22s
	6h 34m 4s

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