Getting error: use of undeclared identifier 'u' when trying to build for iOS

i was trying to test a project on an iOS device.
I first did openfl test cpp and all worked fine.
the openfl update ios -xcode also works without errors.
But when I run the build command in iOS I get a
Error: /Users/lyman/Documents/SDKs/Haxelib/hxcpp/4,0,19/src/Array.cpp:390:28: error: use of undeclared identifier 'u' error.
the line of code in question reads: memcpy(buf+pos,u"null",8);

Any thoughts on that?

This is a hxcpp issue that comes about because of the unicode work on Haxe 4. Until it’s fixed, you can disable the new feature, and get iOS compiling again, by including this in your OpenFL project file.

<haxeflag name="-D" value="disable-unicode-strings" />