Currently dumpCheckin passes a null object to create
the contructor of NetworkStatsCollection.Key but the
constructor requires non-null object. Thus, it caused
the NPE in dumpCheckin. To fix this exception, create
an NetworkIdentitySet() object instead of using an
null object.
Bug: 225131008
Bug: 226539404
Test: dumpsys netstats --checkin is fine
FrameworksNetTests
Change-Id: I7f2dadf0647b3f42e0f667d96291d2ae37e23faf
c3a43b4063