Fixed warning.

Author: Edward Smith

Branch-SDK/Branch-SDK/BNCApplication.h

@@ -50,5 +50,5 @@
 @property (atomic, readonly) NSDictionary<NSString*, NSString*>*_Nonnull deviceKeyIdentityValueDictionary;
 
 /// The team identifier for the app.
-@property (atomic, readonly) NSString* teamID;
+@property (atomic, readonly) NSString*_Nullable teamID;
 @end