Respond to CR.

Signal/src/ViewControllers/NewGroupViewController.m

@@ -46,7 +46,7 @@ NS_ASSUME_NONNULL_BEGIN
 @property (nonatomic, readonly) AvatarImageView *avatarView;
 @property (nonatomic, readonly) UITextField *groupNameTextField;
 
-@property (nonatomic) NSData *groupId;
+@property (nonatomic, readonly) NSData *groupId;
 
 @property (nonatomic, nullable) UIImage *groupAvatar;
 @property (nonatomic) NSMutableSet<NSString *> *memberRecipientIds;
@@ -86,7 +86,7 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (void)commonInit
 {
-    self.groupId = [Randomness generateRandomBytes:16];
+    _groupId = [Randomness generateRandomBytes:16];
 
     _messageSender = SSKEnvironment.shared.messageSender;
     _contactsViewHelper = [[ContactsViewHelper alloc] initWithDelegate:self];

SignalMessaging/utils/OWSContactAvatarBuilder.m

@@ -71,6 +71,8 @@ NS_ASSUME_NONNULL_BEGIN
     return [self initWithContactId:colorSeed name:nonSignalName colorName:(NSString *)colorName diameter:diameter];
 }
 
+#pragma mark - Dependencies
+
 + (OWSContactsManager *)contactsManager
 {
     return (OWSContactsManager *)SSKEnvironment.shared.contactsManager;

SignalMessaging/utils/OWSGroupAvatarBuilder.m

@@ -33,16 +33,20 @@ NS_ASSUME_NONNULL_BEGIN
     return self;
 }
 
-- (nullable UIImage *)buildSavedImage
-{
-    return self.thread.groupModel.groupImage;
-}
+#pragma mark - Dependencies
 
 + (OWSContactsManager *)contactsManager
 {
     return (OWSContactsManager *)SSKEnvironment.shared.contactsManager;
 }
 
+#pragma mark -
+
+- (nullable UIImage *)buildSavedImage
+{
+    return self.thread.groupModel.groupImage;
+}
+
 - (nullable UIImage *)buildDefaultImage
 {
     return [self.class defaultAvatarForGroupId:self.thread.groupModel.groupId
@@ -67,6 +71,7 @@ NS_ASSUME_NONNULL_BEGIN
     UIImage *_Nullable image =
         [OWSGroupAvatarBuilder groupAvatarImageWithBackgroundColor:backgroundColor diameter:diameter];
     if (!image) {
+        OWSFailDebug(@"Could not create group avatar.");
         return nil;
     }