GTBlameHunk nullability

Author: Ben Chatelain

ObjectiveGit/GTBlameHunk.h

@@ -12,21 +12,27 @@
 @class GTOID;
 @class GTSignature;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /// A `GTBlameHunk` is an object that provides authorship info for a set of lines in a `GTBlame`.
 @interface GTBlameHunk : NSObject
 
 /// Designated initializer.
-- (instancetype)initWithGitBlameHunk:(git_blame_hunk)hunk NS_DESIGNATED_INITIALIZER;
+///
+/// hunk - A git_blame_hunk to wrap. May not be NULL.
+///
+/// Returns a blame hunk, or nil if initialization failed.
+- (nullable instancetype)initWithGitBlameHunk:(git_blame_hunk)hunk NS_DESIGNATED_INITIALIZER;
 
 /// A NSRange where `location` is the (1 based) starting line number,
 /// and `length` is the number of lines in the hunk.
 @property (nonatomic, readonly) NSRange lines;
 
 /// The OID of the commit where this hunk was last changed.
-@property (nonatomic, readonly, copy) GTOID *finalCommitOID;
+@property (nonatomic, readonly, copy, nullable) GTOID *finalCommitOID;
 
 /// The signature of the commit where this hunk was last changed.
-@property (nonatomic, readonly) GTSignature *finalSignature;
+@property (nonatomic, readonly, nullable) GTSignature *finalSignature;
 
 /// The path of the file in the original commit.
 @property (nonatomic, readonly, copy) NSString *originalPath;
@@ -39,3 +45,5 @@
 @property (nonatomic, readonly) git_blame_hunk git_blame_hunk;
 
 @end
+
+NS_ASSUME_NONNULL_END