ubiquity crashes once user double click wpa enterprise access point in network manager widget

Ref LP: #1107935

During wireless configuration, ubiquity crashes once double click SSID which is a wpa-enterprise access pointer.

 Traceback (most recent call last):
   File "/usr/lib/ubiquity/ubiquity/frontend/gtk_components/nmwidgets.py", line 170, in row_activated
     self.connect_to_selection(passphrase)
   File "/usr/lib/ubiquity/ubiquity/frontend/gtk_components/nmwidgets.py", line 252, in connect_to_selection
     self.wifi_model.connect_to_ap(model[parent][0], ssid, passphrase)
   File "/usr/lib/ubiquity/ubiquity/nm.py", line 181, in connect_to_ap
     signature='a{sa{sv}}oo'))
   File "/usr/lib/python3/dist-packages/dbus/proxies.py", line 145, in __call__
     **keywords)
   File "/usr/lib/python3/dist-packages/dbus/connection.py", line 651, in call_blocking
     message, timeout)
 dbus.exceptions.DBusException: org.freedesktop.NetworkManager.Settings.Connection.Failed: Failed to determine AP security information

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubiquity-frontend-gtk 2.21.63.3somerville1
ProcVersionSignature: Ubuntu 4.4.0-73.94-generic 4.4.59
Uname: Linux 4.4.0-73-generic x86_64
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
Date: Mon Sep 11 10:00:13 2017
DistributionChannelDescriptor:
 # This is a distribution channel descriptor
 # For more information see http://wiki.ubuntu.com/DistributionChannelDescriptor
 canonical-oem-somerville-xenial-amd64-rebase-20170523-1
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz.efi uuid=879A-B0CF modprobe.blacklist=cdc_mbim blacklist=r8169 modprobe.blacklist=r8169 nomodeset boot=casper automatic-ubiquity noprompt quiet splash ---
InstallationDate: Installed on 2017-09-11 (0 days ago)
InstallationMedia: Ubuntu 16.04 "Xenial" - Build amd64 LIVE Binary 20170523-06:09
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)