Looks like you are using your `mGoogleApiClient` before it is initialized. The initialization of :
private Location mLastLocation = LocationServices.FusedLocationApi.getLastLocation(mGoogleApiClient);
should be done after you have initialized `mGoogleApiClient` in `onCreate`.
So change to
private Location mLastLocation;
and add
mLastLocation = LocationServices.FusedLocationApi.getLastLocation(mGoogleApiClient);
in your `onCreate` after `buildGoogleApiClient`();

Looks like you are using your `mGoogleApiClient` before it is initialized. The initialization of
private Location mLastLocation = LocationServices.FusedLocationApi.getLastLocation(mGoogleApiClient); should be done after you have initialized `mGoogleApiClient` in `onCreate`.
So change to
private Location mLastLocation; and add
mLastLocation = LocationServices.FusedLocationApi.getLastLocation(mGoogleApiClient); in your `onCreate` after `buildGoogleApiClient();`