NS_ASSUME_NONNULL_BEGIN Macro

I am following an online tutorial from team tree house and one of the steps is to create an NSManagedObject subclass for my data model.

When I did that the code automatically generated a class and set of macros at the beginning and and the end:

NS_ASSUME_NONNULL_BEGIN

NS_ASSUME_NONNULL_END

I was searching online but I could not find any documentation about that these guys are doing here. By the way they were defined in the header NSObjCRuntime.h

Any ideas what are they doing?

Thanks a lot in advance :)