diff --git a/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadHelper.java b/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadHelper.java
index 0fa0cac677..928ffadc4f 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadHelper.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadHelper.java
@@ -270,8 +270,8 @@ public final class DownloadHelper {
    * @param dataSourceFactory A {@link DataSource.Factory} used to load the manifest.
    * @param renderersFactory A {@link RenderersFactory} creating the renderers for which tracks are
    *     selected.
-   * @param drmSessionManager An optional {@link DrmSessionManager} used by the renderers created by
-   *     {@code renderersFactory}.
+   * @param drmSessionManager An optional {@link DrmSessionManager}. Used to help determine which
+   *     tracks can be selected.
    * @param trackSelectorParameters {@link DefaultTrackSelector.Parameters} for selecting tracks for
    *     downloading.
    * @return A {@link DownloadHelper} for DASH streams.
@@ -340,8 +340,8 @@ public final class DownloadHelper {
    * @param dataSourceFactory A {@link DataSource.Factory} used to load the playlist.
    * @param renderersFactory A {@link RenderersFactory} creating the renderers for which tracks are
    *     selected.
-   * @param drmSessionManager An optional {@link DrmSessionManager} used by the renderers created by
-   *     {@code renderersFactory}.
+   * @param drmSessionManager An optional {@link DrmSessionManager}. Used to help determine which
+   *     tracks can be selected.
    * @param trackSelectorParameters {@link DefaultTrackSelector.Parameters} for selecting tracks for
    *     downloading.
    * @return A {@link DownloadHelper} for HLS streams.
@@ -410,8 +410,8 @@ public final class DownloadHelper {
    * @param dataSourceFactory A {@link DataSource.Factory} used to load the manifest.
    * @param renderersFactory A {@link RenderersFactory} creating the renderers for which tracks are
    *     selected.
-   * @param drmSessionManager An optional {@link DrmSessionManager} used by the renderers created by
-   *     {@code renderersFactory}.
+   * @param drmSessionManager An optional {@link DrmSessionManager}. Used to help determine which
+   *     tracks can be selected.
    * @param trackSelectorParameters {@link DefaultTrackSelector.Parameters} for selecting tracks for
    *     downloading.
    * @return A {@link DownloadHelper} for SmoothStreaming streams.
@@ -439,27 +439,27 @@ public final class DownloadHelper {
 
   /**
    * Equivalent to {@link #createMediaSource(DownloadRequest, Factory, DrmSessionManager)
-   * createMediaSource(downloadRequest, dataSourceFactory,
-   * DrmSessionManager.getDummyDrmSessionManager())}.
+   * createMediaSource(downloadRequest, dataSourceFactory, null)}.
    */
   public static MediaSource createMediaSource(
       DownloadRequest downloadRequest, DataSource.Factory dataSourceFactory) {
-    return createMediaSource(
-        downloadRequest, dataSourceFactory, DrmSessionManager.getDummyDrmSessionManager());
+    return createMediaSource(downloadRequest, dataSourceFactory, /* drmSessionManager= */ null);
   }
 
   /**
-   * Utility method to create a MediaSource which only contains the tracks defined in {@code
+   * Utility method to create a {@link MediaSource} that only exposes the tracks defined in {@code
    * downloadRequest}.
    *
    * @param downloadRequest A {@link DownloadRequest}.
    * @param dataSourceFactory A factory for {@link DataSource}s to read the media.
-   * @return A MediaSource which only contains the tracks defined in {@code downloadRequest}.
+   * @param drmSessionManager An optional {@link DrmSessionManager} to be passed to the {@link
+   *     MediaSource}.
+   * @return A {@link MediaSource} that only exposes the tracks defined in {@code downloadRequest}.
    */
   public static MediaSource createMediaSource(
       DownloadRequest downloadRequest,
       DataSource.Factory dataSourceFactory,
-      DrmSessionManager<?> drmSessionManager) {
+      @Nullable DrmSessionManager<?> drmSessionManager) {
     @Nullable Constructor<? extends MediaSourceFactory> constructor;
     switch (downloadRequest.type) {
       case DownloadRequest.TYPE_DASH:
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadService.java b/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadService.java
index f830a7d792..51f7fa3765 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadService.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadService.java
@@ -595,7 +595,7 @@ public abstract class DownloadService extends Service {
   }
 
   @Override
-  public int onStartCommand(Intent intent, int flags, int startId) {
+  public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
     lastStartId = startId;
     taskRemoved = false;
     @Nullable String intentAction = null;
@@ -617,7 +617,9 @@ public abstract class DownloadService extends Service {
         // Do nothing.
         break;
       case ACTION_ADD_DOWNLOAD:
-        @Nullable DownloadRequest downloadRequest = intent.getParcelableExtra(KEY_DOWNLOAD_REQUEST);
+        @Nullable
+        DownloadRequest downloadRequest =
+            Assertions.checkNotNull(intent).getParcelableExtra(KEY_DOWNLOAD_REQUEST);
         if (downloadRequest == null) {
           Log.e(TAG, "Ignored ADD_DOWNLOAD: Missing " + KEY_DOWNLOAD_REQUEST + " extra");
         } else {
@@ -642,7 +644,7 @@ public abstract class DownloadService extends Service {
         downloadManager.pauseDownloads();
         break;
       case ACTION_SET_STOP_REASON:
-        if (!intent.hasExtra(KEY_STOP_REASON)) {
+        if (!Assertions.checkNotNull(intent).hasExtra(KEY_STOP_REASON)) {
           Log.e(TAG, "Ignored SET_STOP_REASON: Missing " + KEY_STOP_REASON + " extra");
         } else {
           int stopReason = intent.getIntExtra(KEY_STOP_REASON, /* defaultValue= */ 0);
@@ -650,7 +652,9 @@ public abstract class DownloadService extends Service {
         }
         break;
       case ACTION_SET_REQUIREMENTS:
-        @Nullable Requirements requirements = intent.getParcelableExtra(KEY_REQUIREMENTS);
+        @Nullable
+        Requirements requirements =
+            Assertions.checkNotNull(intent).getParcelableExtra(KEY_REQUIREMENTS);
         if (requirements == null) {
           Log.e(TAG, "Ignored SET_REQUIREMENTS: Missing " + KEY_REQUIREMENTS + " extra");
         } else {