Add missing generic types and nullability annotations to PFACLState.

Author: nlutsenko

Parse/Internal/ACL/State/PFACLState.h

@@ -17,7 +17,7 @@ typedef void (^PFACLStateMutationBlock)(PFMutableACLState *);
 
 @interface PFACLState : PFBaseState<PFBaseStateSubclass, NSCopying, NSMutableCopying>
 
-@property (nonatomic, copy, readonly) NSDictionary *permissions;
+@property (nonatomic, copy, readonly) NSDictionary<NSString *, id> *permissions;
 @property (nonatomic, assign, readonly, getter=isShared) BOOL shared;
 
 ///--------------------------------------

Parse/Internal/ACL/State/PFMutableACLState.h

@@ -9,9 +9,13 @@
 
 #import "PFACLState.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface PFMutableACLState : PFACLState
 
-@property (nonatomic, copy, readwrite) NSMutableDictionary *permissions;
+@property (nonatomic, copy, readwrite) NSMutableDictionary<NSString *, id> *permissions;
 @property (nonatomic, assign, readwrite, getter=isShared) BOOL shared;
 
 @end
+
+NS_ASSUME_NONNULL_END

Parse/Internal/ACL/State/PFMutableACLState.m

@@ -22,7 +22,7 @@ @implementation PFMutableACLState
 
 - (instancetype)init {
     self = [super init];
-    if (!self) return nil;
+    if (!self) return self;
 
     _permissions = [NSMutableDictionary dictionary];