It might come in handy in case you want to restore the phone's original ROM or save yourself from a phone brick , just flash it via Flashtool.
Tested myself and it works.
For the newbies: while flashing it via Flashtool you need to press VolDow and plug in the usb to enter flashmode (green led), the image shown in the process might confuse you...
Download: Xperia_Go_ST27i_6.1.1.B.1.1.0_Sony.ftf (362MB)
If it helps, please press THANKS.