Deal with UserState#getEnabledPrintServices returning null.

                        // to handle it as the change may affect ongoing print jobs.

                        UserState userState = getOrCreateUserStateLocked(getChangingUserId());

                        boolean stoppedSomePackages = false;

                        Iterator<PrintServiceInfo> iterator = userState.getEnabledPrintServices()

                                .iterator();

                        List<PrintServiceInfo> enabledServices = userState

                                .getEnabledPrintServices();

                        if (enabledServices == null) {

                            return false;

                        }

                        Iterator<PrintServiceInfo> iterator = enabledServices.iterator();

                        while (iterator.hasNext()) {

                            ComponentName componentName = iterator.next().getComponentName();

                            String componentPackage = componentName.getPackageName();

import static android.content.pm.PackageManager.GET_SERVICES;

import static android.content.pm.PackageManager.MATCH_DEBUG_TRIAGED_MISSING;

import android.annotation.Nullable;

import android.app.PendingIntent;

import android.content.ComponentName;

import android.content.Context;

        mSpooler.setPrintJobState(printJobId, PrintJobInfo.STATE_QUEUED, null);

    }

    public List<PrintServiceInfo> getEnabledPrintServices() {

    public @Nullable List<PrintServiceInfo> getEnabledPrintServices() {

        synchronized (mLock) {

            List<PrintServiceInfo> enabledServices = null;

            final int installedServiceCount = mInstalledServices.size();