Ok guys, maybe this could work for those who lost their IMEI running a "fastboot erase all" or for any other reason. It's a theoretical solution, since I can't test it on my device because my IMEI works. So don't blame me if doesn't work.
1) Go on fastboot mode (vol down + power button) and select BP Tools
2) Connect the usb cable to computer
3) Open Windows Device Manager (write "devmgmt.msc" without quotes in the Start menu)
4) You will see "Motorola QC Diag Interface, click on it and update drivers, search driver on computer, manually search, PORTS (com and lpt), Motorola, Motorola QC Diag Port
5) Now your device is correctly recognized
6) download this tool (credits to lyriquidperfection, the tool isn't mine)
10) extract and open the tool, select Qualcomm NV tools
11) chose the right com port, connect your phone and go on secure options, check IMEI box, click Read (should be 000000000000000)
12) write your IMEI and click Write
13) tell me if it works
TESTED, UNFORTUNATELY IT DOESN'T WORK.
This thread can be closed.