Nexus 5 : IMEI 0 issue

Sometime back, an update (believe me, an OTA update) blocked all network calls on my mobile. After struggling for a while, I came to know that IMEI of my phone was set to 0. Tried many solutions (resetting the phone, clearing cache, even installing fresh OS), but none came to my rescue.

Thanks to a guy (sorry for not crediting), who uploaded instructions in Russian language, and with the help of Google Translate, my phone is up and running again.

Note: Before proceeding any further, keep in mind that you need IMEI of your phone (check on back panel)

Download related files from here.

Here is the procedure that I've followed:

1. Install the LG driver LG
2. Install QPST
3. Copy the entire folder EFS Professional to C drive
4. Unpack the archive Nexus5 the root of drive C.
5. Using WUG Nexus toolkit:
1. Make sure running stock Android 5.0.1
2. Rooted
3. If necessary, you can reset the IMEI using backups zero IMEI from the archive. To do this, simply make a backup of your EFS in TWRP, then replace in the folder's backup your files on the distribution of similar make and restore EFS.
1. If it is already erased and writes 0, then just skip this step.
4. Advanced tools: 
1. Install boot(kernel) 5.0.0_diag_BOOT.img from folder
2. open a command window, and run the following command
• adb shell > su > setprop sys.usb.config diag,adb
3. This activates the diagnostic mode on the phone and will be available operations with nvram through com port.
6. Open EFS Professional:
1. Click on Qualcomm NV Tools, Hit connect and go to Secure Ops.
2. Hit Read and check off imei and meid, and enter imei and meid (meid is just imei without last two digits)
3. Hit Write
4. Reboot phone and check imei by typing *#06# 
5. If imei still 0 > do b above again, then Read (note esn now appears), then Write again (ignore the errors) > Reboot and check, should be working.
6. Repair 3G/LTE:
7. Install the diagnostic bootloader again and run the setprop shell command again
8. Open QPST Configuration from Windows programs
9. Click Ports tab, Add new port, deselect secure ports only and should now see the serial port with phone connected (if not, then the serial drivers aren’t installed properly à Use WUG driver support to remove all android drivers and plug the phone in again to install from windows update)
10. Click Start Start Clients > Software Download
11. Go to Backup tab and click Start Leave SPC with all zeros (note file location of backup)
12. Go to Restore tab, check “Allow phone / file ESN mismatch”, restore from the NEXUS5.qcn (from the folder), again leave SPC with all zeros here
• Now click Browse next to QCN File, locate the backup from j above and now enter in SPC: 308508 > Start
13. Reboot phone > everything should be working!
7. Don't forget to make a complete EFS backup now!!!