@Override
        public String toString() {
            return this.value;
        }
It is recommended to use {@link AckEventType#getRawValue()} to get the string value of the enum as the value
returned by this toString method may be null when the enum value is {@link #SDK_UNKNOWN}.
aws-java-sdk-kinesisvideo/src/main/java/com/amazonaws/services/kinesisvideo/model/AckEventType.java