Fail fingerprint enroll with error if HAT is null

Fingerprint enroll expects a non-null HAT. If we don't have one, rather
than crashing or stalling out enrollment, fail fast with an error.

Test: Manual

Bug: 193811614
Change-Id: Ifb791e19430e33cb82566e4916ab1a7b997b32ff

src/com/android/settings/biometrics/fingerprint/FingerprintEnrollSidecar.java

@@ -19,7 +19,9 @@ package com.android.settings.biometrics.fingerprint;
 import android.app.Activity;
 import android.app.settings.SettingsEnums;
 import android.hardware.fingerprint.FingerprintManager;
+import android.util.Log;
 
+import com.android.settings.R;
 import com.android.settings.Utils;
 import com.android.settings.biometrics.BiometricEnrollSidecar;
 
@@ -27,6 +29,7 @@ import com.android.settings.biometrics.BiometricEnrollSidecar;
  * Sidecar fragment to handle the state around fingerprint enrollment.
  */
 public class FingerprintEnrollSidecar extends BiometricEnrollSidecar {
+    private static final String TAG = "FingerprintEnrollSidecar";
 
     private FingerprintManager mFingerprintManager;
     private @FingerprintManager.EnrollReason int mEnrollReason;
@@ -40,6 +43,14 @@ public class FingerprintEnrollSidecar extends BiometricEnrollSidecar {
     @Override
     protected void startEnrollment() {
         super.startEnrollment();
+
+        if (mToken == null) {
+            Log.e(TAG, "Null hardware auth token for enroll");
+            onEnrollmentError(FingerprintManager.FINGERPRINT_ERROR_HW_UNAVAILABLE,
+                    getString(R.string.fingerprint_intro_error_unknown));
+            return;
+        }
+
         mFingerprintManager.enroll(mToken, mEnrollmentCancel, mUserId, mEnrollmentCallback,
                 mEnrollReason);
     }