Caution around group avatars.

SignalServiceKit/src/Messages/OWSMessageManager.m

@@ -1153,7 +1153,9 @@ NS_ASSUME_NONNULL_BEGIN
     [message updateWithSendingToSingleGroupRecipient:envelope.source transaction:transaction];
 
     if (gThread.groupModel.groupImage) {
-        NSData *data = UIImagePNGRepresentation(gThread.groupModel.groupImage);
+        NSData *_Nullable data = UIImagePNGRepresentation(gThread.groupModel.groupImage);
+        OWSAssertDebug(data);
+        if (data) {
             DataSource *_Nullable dataSource = [DataSourceValue dataSourceWithData:data fileExtension:@"png"];
             [self.messageSenderJobQueue addMediaMessage:message
                                              dataSource:dataSource
@@ -1162,7 +1164,7 @@ NS_ASSUME_NONNULL_BEGIN
                                                 caption:nil
                                          albumMessageId:nil
                                   isTemporaryAttachment:YES];
-
+        }
     } else {
         [self.messageSenderJobQueue addMessage:message transaction:transaction];
     }