Clean up ahead of PR.

SignalServiceKit/src/Util/NSData+hexString.m

@@ -1,9 +1,5 @@
 //
-//  NSData+hexString.m
+//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
-//  TextSecureKit
-//
-//  Created by Frederic Jacobs on 28/10/14.
-//  Copyright (c) 2014 Open Whisper Systems. All rights reserved.
 //
 
 #import "NSData+hexString.h"
@@ -13,8 +9,9 @@
 - (NSString *)hexadecimalString {
     /* Returns hexadecimal string of NSData. Empty string if data is empty. */
     const unsigned char *dataBuffer = (const unsigned char *)[self bytes];
-    if (!dataBuffer)
+    if (!dataBuffer) {
-        return [NSString string];
+        return @"";
+    }
 
     NSUInteger dataLength = [self length];
     NSMutableString *hexString = [NSMutableString stringWithCapacity:(dataLength * 2)];
@@ -22,7 +19,7 @@
     for (NSUInteger i = 0; i < dataLength; ++i) {
         [hexString appendFormat:@"%02x", dataBuffer[i]];
     }
-    return [NSString stringWithString:hexString];
+    return [hexString copy];
 }
 
 @end