Respond to CR.

// FREEBIE

Signal/src/contact/OWSContactsManager.m

@@ -589,7 +589,7 @@ void onAddressBookChanged(ABAddressBookRef notifyAddressBook, CFDictionaryRef in
 
 - (BOOL)hasAddressBook
 {
-    return self.addressBookReference;
+    return (BOOL)self.addressBookReference;
 }
 
 #pragma mark - Logging

Signal/src/util/OWSContactsSyncing.h

@@ -4,6 +4,8 @@
 
 #import "SignalsViewController.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @class OWSContactsManager;
 @class OWSMessageSender;
 
@@ -13,3 +15,5 @@
                           messageSender:(OWSMessageSender *)messageSender;
 
 @end
+
+NS_ASSUME_NONNULL_END

Signal/src/util/OWSContactsSyncing.m

@@ -11,6 +11,8 @@
 #import <SignalServiceKit/TSAccountManager.h>
 #import <SignalServiceKit/TSStorageManager.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 NSString *const kTSStorageManagerOWSContactsSyncingCollection = @"kTSStorageManagerOWSContactsSyncingCollection";
 NSString *const kTSStorageManagerOWSContactsSyncingLastMessageKey =
     @"kTSStorageManagerOWSContactsSyncingLastMessageKey";
@@ -56,6 +58,8 @@ NSString *const kTSStorageManagerOWSContactsSyncingLastMessageKey =
 
 - (void)sendSyncContactsMessageIfNecessary
 {
+    AssertIsOnMainThread();
+
     if (self.isRequestInFlight) {
         // De-bounce.  It's okay if we ignore some new changes;
         // `sendSyncContactsMessageIfPossible` is called fairly
@@ -104,6 +108,8 @@ NSString *const kTSStorageManagerOWSContactsSyncingLastMessageKey =
 
 - (void)sendSyncContactsMessageIfPossible
 {
+    AssertIsOnMainThread();
+
     if (![self.contactsManager hasAddressBook]) {
         // Don't bother until the contacts manager has finished setup.
         return;
@@ -130,3 +136,5 @@ NSString *const kTSStorageManagerOWSContactsSyncingLastMessageKey =
 }
 
 @end
+
+NS_ASSUME_NONNULL_END