Fix error in Actionscript

I have a desktop Actionscript project. The following line _rXML.part.instrument.(@id = instruments[@id]); Produces the error "Access of possibly undefined property id" What is odd is that this error only occurs on OSX. The exact same code in Windows runs fine. The Mac is running InteliJ / Catalina and Windows is running FB 4.7. Both are using SDK v32 and I think this error comes from the compiler so the different environment should not matter. All I am trying to do is recompile an existing application. On an older mac, pre Catalina using FB4.7 the code works fine.