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