diff --git a/library/core/src/main/java/com/google/android/exoplayer2/drm/DefaultDrmSessionManager.java b/library/core/src/main/java/com/google/android/exoplayer2/drm/DefaultDrmSessionManager.java
index 3820836e49..fb684f627f 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/drm/DefaultDrmSessionManager.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/drm/DefaultDrmSessionManager.java
@@ -544,7 +544,7 @@ public class DefaultDrmSessionManager<T extends ExoMediaCrypto> implements DrmSe
     @Override
     public void onEvent(
         ExoMediaDrm<? extends T> md,
-        byte[] sessionId,
+        @Nullable byte[] sessionId,
         int event,
         int extra,
         @Nullable byte[] data) {
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/drm/ExoMediaDrm.java b/library/core/src/main/java/com/google/android/exoplayer2/drm/ExoMediaDrm.java
index 49915f3af5..6bd8d9688f 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/drm/ExoMediaDrm.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/drm/ExoMediaDrm.java
@@ -80,7 +80,7 @@ public interface ExoMediaDrm<T extends ExoMediaCrypto> {
      */
     void onEvent(
         ExoMediaDrm<? extends T> mediaDrm,
-        byte[] sessionId,
+        @Nullable byte[] sessionId,
         int event,
         int extra,
         @Nullable byte[] data);
@@ -215,6 +215,7 @@ public interface ExoMediaDrm<T extends ExoMediaCrypto> {
       throws NotProvisionedException;
 
   /** @see MediaDrm#provideKeyResponse(byte[], byte[]) */
+  @Nullable
   byte[] provideKeyResponse(byte[] scope, byte[] response)
       throws NotProvisionedException, DeniedByServerException;
 
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/drm/FrameworkMediaDrm.java b/library/core/src/main/java/com/google/android/exoplayer2/drm/FrameworkMediaDrm.java
index 615aa0e7b1..2cb7e66a2c 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/drm/FrameworkMediaDrm.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/drm/FrameworkMediaDrm.java
@@ -84,8 +84,6 @@ public final class FrameworkMediaDrm implements ExoMediaDrm<FrameworkMediaCrypto
     }
   }
 
-  // FIXME: incompatible types in argument.
-  @SuppressWarnings("nullness:argument.type.incompatible")
   @Override
   public void setOnEventListener(
       final ExoMediaDrm.OnEventListener<? super FrameworkMediaCrypto> listener) {
@@ -160,8 +158,7 @@ public final class FrameworkMediaDrm implements ExoMediaDrm<FrameworkMediaCrypto
     return new KeyRequest(requestData, licenseServerUrl);
   }
 
-  // FIXME: incompatible types in return.
-  @SuppressWarnings("nullness:return.type.incompatible")
+  @Nullable
   @Override
   public byte[] provideKeyResponse(byte[] scope, byte[] response)
       throws NotProvisionedException, DeniedByServerException {
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/scheduler/PlatformScheduler.java b/library/core/src/main/java/com/google/android/exoplayer2/scheduler/PlatformScheduler.java
index e6679e1a5a..752239c991 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/scheduler/PlatformScheduler.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/scheduler/PlatformScheduler.java
@@ -25,6 +25,7 @@ import android.content.Context;
 import android.content.Intent;
 import android.os.PersistableBundle;
 import androidx.annotation.RequiresPermission;
+import com.google.android.exoplayer2.util.Assertions;
 import com.google.android.exoplayer2.util.Log;
 import com.google.android.exoplayer2.util.Util;
 
@@ -129,9 +130,8 @@ public final class PlatformScheduler implements Scheduler {
         logd("Requirements are met");
         String serviceAction = extras.getString(KEY_SERVICE_ACTION);
         String servicePackage = extras.getString(KEY_SERVICE_PACKAGE);
-        // FIXME: incompatible types in argument.
-        @SuppressWarnings("nullness:argument.type.incompatible")
-        Intent intent = new Intent(serviceAction).setPackage(servicePackage);
+        Intent intent =
+            new Intent(Assertions.checkNotNull(serviceAction)).setPackage(servicePackage);
         logd("Starting service action: " + serviceAction + " package: " + servicePackage);
         Util.startForegroundService(this, intent);
       } else {