Fix NullPointerException in PackageManagerService

Add null check before calling equals() on packageName to prevent a
potential NullPointerException that could cause system restart.

When executing certain package manager service calls, packageName could
be null, leading to a fatal exception in the system process. This change
adds a null check before the equals() invocation to safely handle the
null case.

Test: Manual testing with service call, no crash observed
Change-Id: Idbbff663cc68614677a2c0d21a8941c4d9c7dd04
Signed-off-by: Jia Jia <jia.jia@zte.com.cn>
Signed-off-by: MOVZX <movzx@yahoo.com>

services/core/java/com/android/server/pm/PackageManagerService.java

@@ -3410,7 +3410,7 @@ public class PackageManagerService implements PackageSender, TestUtilityService
                 // TODO Do we have to do it even if userId != UserHandle.USER_ALL?  Otherwise,
                 // this check is probably not needed, since DO should be registered as a device
                 // admin on some user too. (Original bug for this: b/17657954)
-                if (packageName.equals(deviceOwnerPackageName)) {
+                if (packageName != null && packageName.equals(deviceOwnerPackageName)) {
                     return true;
                 }
                 // Does it contain a device admin for any user?