Adding nulls check in various drop-drop events

The original patch by motorola had another check, but the 2nd check
is wrong as in that case, there would be a nullpointer exception just
after the check for the same reason.

issue: 15518908
issue: 15516428

Change-Id: I85c5fb3541b7f837e6c5295e97e45162a4120e39
1 file changed