Warnings in SharkORM.h with Xcode 11 due to missing nullability type specifier

[ianhlavats]

When linking against SharkORM using CocoaPods, Xcode reports warnings in SharkORM.h due to missing nullability type specifier:

Warning: Pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified) File: Pods/SharkORM/SharkORM/SharkORM.h:261

The issue is related to these lines of code:

@interface SRKRelationship : NSObject {
    
}
@property Class                                       sourceClass;
@property Class                                       targetClass;

After studying the code, it appears SharkORM expects that these properties could be nil at some point so I think the solution to remove these compilation warnings would be:

@interface SRKRelationship : NSObject {
    
}
@property Class _Nullable                             sourceClass;
@property Class _Nullable                             targetClass;

Will submit a PR.

[editfmah]

It is unlikely that these values will ever be null, but I think they are constructed from both ends of the relationship so would probably upset the compiler with the code in it's current form.

[ianhlavats]

Thanks for merging... can you create a new release?