For non-telephony, non-wifi networks, both extraInfo and SSID are likely
to be null, in which case
getString(network_available_sign_in_detailed, null) would be used for
the notification contents, which would just print "null" (by default the
string template is just "%1$s").
Use an empty string instead, as there is no string identifier for the
network. This should still be better than having text that says "null".
Test: atest
Bug: 334926818
Change-Id: I19bdba186d2402b40549b1ad5f97864b7c38ca10
05aa33ccec