How to restore the IMEI number on the Samsung Galaxy S4 I9505? (IMEI=Unknown, Baseband=Unknown, Sim Card Not Detected) Information:

Hello, I lost my IMEI number on my Samsung Galaxy S4 GT-I9505 today and I would like to restore my original IMEI back to my phone. I still have my original IMEI of my phone written down. And my Sim Card is not detected.

I do not have any backups!
I didn't make any backups of /efs (sorry!), will do that when I have this problem fixed and backup it on all my computers. 

I have searched Google and www.Android.StackExchange.com but couldn't find anything that worked for me. (So please don't mark this as a duplicate question)



In short:


Samsung Galaxy S4 GT-I9505
I live in The Netherlands
My carrier is KPN (if you wanted to know that)
I have my IMEI number written down
I do not have any backups of /efs! (sorry!)
IMEI = Unknown
Baseband = Unknown
Sim Card not detected




Screenshots:

I dialed *#06# to get the IMEI number:



The hidden menu in Android: (*#*#4636#*#* or *#*#INFO#*#*):





What I have tried:


Of course, I flashed the stock ROM back on my phone. (Android 4.4.2)
I downloaded a backup of /efs from someone else on the internet and flashed that on my phone. However the IMEI is still "Unknown".
When I flash the stock ROM on my phone for my country (The Netherlands), it did restore my IMEI. However WIFI didn't work on the stock ROM, and when I flash Cyanogenmod back on my phone, I don't have an IMEI anymore. (So I think the IMEI wasn't written permanently on my phone).




Any help is appreciated.
If I need to add some more information, just tell me. Thanks!
After all this was a simple bug in the cm12.1-20150623 nightly. It has been fixed in the cm12.1-20150629 nightly. For more information about this bug you look here: CM12.1 Nightly no Sim found. For all the people helped me so far, thanks for your support.