Fix possible NPE in DPMS.

If there's no ActiveAdmin for the given user then the ternary
expression would return null, which immediately will throw an NPE as it
gets auto-unboxed into from Boolean to boolean.

Bug: 217923092
Test: errorprone build
Change-Id: I4043f0061e5a23e4d5aa408917f6d51b8bbf22ec

services/Android.bp

@@ -17,6 +17,7 @@ java_defaults {
             "-Xep:AndroidFrameworkCompatChange:ERROR",
             // "-Xep:AndroidFrameworkUid:ERROR",
             "-Xep:SelfEquals:ERROR",
+            "-Xep:NullTernary:ERROR",
             // NOTE: only enable to generate local patchfiles
             // "-XepPatchChecks:refaster:frameworks/base/errorprone/refaster/EfficientXml.java.refaster",
             // "-XepPatchLocation:/tmp/refaster/",

services/devicepolicy/java/com/android/server/devicepolicy/DevicePolicyManagerService.java

@@ -6847,7 +6847,7 @@ public class DevicePolicyManagerService extends BaseIDevicePolicyManager {
                 String.format(NOT_SYSTEM_CALLER_MSG, "call isAlwaysOnVpnLockdownEnabledForUser"));
         synchronized (getLockObject()) {
             ActiveAdmin admin = getDeviceOrProfileOwnerAdminLocked(userHandle);
-            return admin != null ? admin.mAlwaysOnVpnLockdown : null;
+            return admin != null && admin.mAlwaysOnVpnLockdown;
         }
     }