Handle null pointer cases in ConnectivityService

If a method is called by adb command "service call"
with no parameters. It will cause to crash because
of a null object reference.

Add a null check for them to avoid system server crash.

Bug: 172885426
Test: FrameworksNetTest
      adb shell service call connectivity #
Change-Id: I8748fc5c6a7a6e82db3581e3026a3f75909a357e