Remove warning suppression.

This was added in https://github.com/google/ExoPlayer/commit/9609af3c23383f2fd5571662d271c3013875705d as part of a LSC.

The RequiresNonNull annotation doesn't work anymore (it doesn't
recognize the outer class member and instead tries to find
the same variable on the inner class). So instead of suppressing
the warning of the non-fulfilled precondition, we can just
check the non-nullness directly and remove the precondition.

PiperOrigin-RevId: 367593941

library/core/src/main/java/com/google/android/exoplayer2/drm/DefaultDrmSessionManager.java

@@ -52,7 +52,6 @@ import java.util.Set;
 import java.util.UUID;
 import java.util.UUID;
 import org.checkerframework.checker.nullness.qual.EnsuresNonNull;
 import org.checkerframework.checker.nullness.qual.EnsuresNonNull;
 import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
-import org.checkerframework.checker.nullness.qual.RequiresNonNull;
 
 
 /**
 /**
  * A {@link DrmSessionManager} that supports playbacks using {@link ExoMediaDrm}.
  * A {@link DrmSessionManager} that supports playbacks using {@link ExoMediaDrm}.
@@ -483,8 +482,6 @@ public class DefaultDrmSessionManager implements DrmSessionManager {
     exoMediaDrm = null;
     exoMediaDrm = null;
   }
   }
 
 
-  // precondition of preacquiredSessionReference.acquire is not satisfied.
-  @SuppressWarnings("nullness:contracts.precondition.not.satisfied")
   @Override
   @Override
   public DrmSessionReference preacquireSession(
   public DrmSessionReference preacquireSession(
       Looper playbackLooper,
       Looper playbackLooper,
@@ -943,13 +940,13 @@ public class DefaultDrmSessionManager implements DrmSessionManager {
      *
      *
      * <p>Must be called at most once. Can be called from any thread.
      * <p>Must be called at most once. Can be called from any thread.
      */
      */
-    @RequiresNonNull("playbackHandler")
     public void acquire(Format format) {
     public void acquire(Format format) {
-      playbackHandler.post(
+      checkNotNull(playbackHandler)
+          .post(
               () -> {
               () -> {
                 if (prepareCallsCount == 0 || isReleased) {
                 if (prepareCallsCount == 0 || isReleased) {
-              // The manager has been fully released or this reference has already been released.
-              // Abort the acquisition attempt.
+                  // The manager has been fully released or this reference has already been
+                  // released. Abort the acquisition attempt.
                   return;
                   return;
                 }
                 }
                 this.session =
                 this.session =