Related to : SMS messages just have "null"

Try this,

delete their contact

then

Settings > Applications > Manage Applications > Select the Messaging App

Choose 'Clear Data' and also 'Clear Cache'.

N.B. you will lose all data / txt msg's in your phone

(don't forget to write their number down to save as new afterwards!)

Do you have delivery reports turned on for mms/sms?

This just happened to me, too bad no one has answered.

That happens if you have multiple devices logged on in the same account. For example in Device A, you've received a message from a person or group chat but you archived it. Then when you open Device B, you will receive the message again but now it will show "null", cause it cant show the message anymore as you archived it or hide it in Device A. That is based on my experience as I always hid messages on my Messenger app. Assuming that you dont know that girl or person, maybe they deleted the chat immediately (you can still delete a message if it was not yet delivered). Or the person had their account deactivated.

Ahh I have the same problem! Obviously not one of the popular problems on these forums since I don't see a lot of posts. So for me, text forwarding was working perfectly but now experiencing same issue after having to erase settings on iPhone to fix another issue from a wonky app. Text message forwarding option shows up on iPhone with toggle switch for each device, but when attempting to connect on Mac, message app opens, but no popup is displayed. When attempting to connect on an iPad it gives: "...enter the code "(null)" on your iPhone now."I've tried logout/login on iMessage all around. Nothing. I've tried logout/login to iCloud login all around. Nothing. I've tried resetting network settings on iPhone. Nothing.(Power cycled each device in between logout/logins.)Tried disabling bluetooth on all devices and repeating. Nothing.Tried disabling wifi (on iPhone only) and bluetooth (all devices) and repeating. Nothing.Continuity is very much working on the devices as Copy/Paste, Phone Calls, etc. are all function perfectly.Running Console on Mac when attempting to pair devices (the enable text message forwarding from iPhone) shows a very clear (and consistent) "Decryption Error" from the identityservicesd library, and public/private decryption failed (yes it includes a frowny face, which is really how I know I'm in trouble). It seems like a key/pointer/something changed/corrupted/who knows, as a result of the reset and now I'm not sure how to get the devices to acknowledge the change or at least look in the same place. Is there a way to reset/update public/private keys for devices for this type of activity? I'm reluctant to start randomly deleting keys from the keychain access (I think I read someone suggested that somewhere). Since I'm a sad newbie to the whole Mac stuff I'm not really sure what to do anymore short of full wipe of everything. Not even sure that would solve the problem if restoring things from backups. Help!