Remove unnecessary null pointer initialization for class variables

In Java, the class variables have default initialization - null
for pointers.

Also, removed unnecessary template arguments when creating templetized
objects:
OLD:
  List<BluetoothDevice> devices = new ArrayList<BluetoothDevice>();
NEW:
  List<BluetoothDevice> devices = new ArrayList<>();

Test: code compilation
Bug: 73205770
Change-Id: Ib983ee40df6bc5bb250ed23fa05a92c6b0365a5a