public static OptionalString ofNullable(ResourceKey key, String value) {
        return new GenericOptionalString(RUNTIME_SOURCE, key, value);
    }
public static OptionalString ofNullable ( ResourceKey key , String value ) { return new GenericOptionalString ( RUNTIME_SOURCE , key , value ) ; }
Returns new instance of OptionalString with given key and value
@param key key of the returned OptionalString
@param value wrapped string
@return given object wrapped in OptionalString with given key