diff --git a/core/api/system-current.txt b/core/api/system-current.txt
index 62ffac7bddf21..d30d59f707362 100644
--- a/core/api/system-current.txt
+++ b/core/api/system-current.txt
@@ -10468,7 +10468,7 @@ package android.service.voice {
     method @RequiresPermission(allOf={android.Manifest.permission.RECORD_AUDIO, android.Manifest.permission.CAPTURE_AUDIO_HOTWORD}) public int setParameter(int, int);
     method @RequiresPermission(allOf={android.Manifest.permission.RECORD_AUDIO, android.Manifest.permission.CAPTURE_AUDIO_HOTWORD}) public boolean startRecognition(int);
     method @RequiresPermission(allOf={android.Manifest.permission.RECORD_AUDIO, android.Manifest.permission.CAPTURE_AUDIO_HOTWORD}) public boolean startRecognition();
-    method @Nullable public boolean startRecognition(@NonNull android.os.ParcelFileDescriptor, @NonNull android.media.AudioFormat, @Nullable android.os.PersistableBundle);
+    method public boolean startRecognition(@NonNull android.os.ParcelFileDescriptor, @NonNull android.media.AudioFormat, @Nullable android.os.PersistableBundle);
     method @RequiresPermission(allOf={android.Manifest.permission.RECORD_AUDIO, android.Manifest.permission.CAPTURE_AUDIO_HOTWORD}) public boolean stopRecognition();
     method public final void updateState(@Nullable android.os.PersistableBundle, @Nullable android.os.SharedMemory);
     field public static final int AUDIO_CAPABILITY_ECHO_CANCELLATION = 1; // 0x1
@@ -10493,7 +10493,7 @@ package android.service.voice {
     method public abstract void onAvailabilityChanged(int);
     method public void onHotwordDetectionServiceInitialized(int);
     method public void onHotwordDetectionServiceRestarted();
-    method public void onRejected(@Nullable android.service.voice.HotwordRejectedResult);
+    method public void onRejected(@NonNull android.service.voice.HotwordRejectedResult);
   }
 
   public static class AlwaysOnHotwordDetector.EventPayload {
@@ -10554,8 +10554,8 @@ package android.service.voice {
   }
 
   public static final class HotwordDetectionService.Callback {
-    method public void onDetected(@Nullable android.service.voice.HotwordDetectedResult);
-    method public void onRejected(@Nullable android.service.voice.HotwordRejectedResult);
+    method public void onDetected(@NonNull android.service.voice.HotwordDetectedResult);
+    method public void onRejected(@NonNull android.service.voice.HotwordRejectedResult);
   }
 
   public interface HotwordDetector {
@@ -10576,7 +10576,7 @@ package android.service.voice {
     method public void onHotwordDetectionServiceRestarted();
     method public void onRecognitionPaused();
     method public void onRecognitionResumed();
-    method public void onRejected(@Nullable android.service.voice.HotwordRejectedResult);
+    method public void onRejected(@NonNull android.service.voice.HotwordRejectedResult);
   }
 
   public final class HotwordRejectedResult implements android.os.Parcelable {
diff --git a/core/java/android/service/voice/AbstractHotwordDetector.java b/core/java/android/service/voice/AbstractHotwordDetector.java
index 48967482fbdfb..54ccf309a58eb 100644
--- a/core/java/android/service/voice/AbstractHotwordDetector.java
+++ b/core/java/android/service/voice/AbstractHotwordDetector.java
@@ -55,10 +55,8 @@ abstract class AbstractHotwordDetector implements HotwordDetector {
     /**
      * Detect hotword from an externally supplied stream of data.
      *
-     * @return a writeable file descriptor that clients can start writing data in the given format.
-     * In order to stop detection, clients can close the given stream.
+     * @return true if the request to start recognition succeeded
      */
-    @Nullable
     @Override
     public boolean startRecognition(
             @NonNull ParcelFileDescriptor audioStream,
diff --git a/core/java/android/service/voice/AlwaysOnHotwordDetector.java b/core/java/android/service/voice/AlwaysOnHotwordDetector.java
index bacc6ec2227b1..e8130172221a5 100644
--- a/core/java/android/service/voice/AlwaysOnHotwordDetector.java
+++ b/core/java/android/service/voice/AlwaysOnHotwordDetector.java
@@ -524,7 +524,7 @@ public class AlwaysOnHotwordDetector extends AbstractHotwordDetector {
          * @param result Info about the second stage detection result, provided by the
          *         {@link HotwordDetectionService}.
          */
-        public void onRejected(@Nullable HotwordRejectedResult result) {
+        public void onRejected(@NonNull HotwordRejectedResult result) {
         }
 
         /**
@@ -1164,7 +1164,7 @@ public class AlwaysOnHotwordDetector extends AbstractHotwordDetector {
         }
 
         @Override
-        public void onRejected(HotwordRejectedResult result) {
+        public void onRejected(@NonNull HotwordRejectedResult result) {
             if (DBG) {
                 Slog.d(TAG, "onRejected(" + result + ")");
             } else {
diff --git a/core/java/android/service/voice/HotwordDetectionService.java b/core/java/android/service/voice/HotwordDetectionService.java
index 473e7ae76cc98..ea01e09ef0de6 100644
--- a/core/java/android/service/voice/HotwordDetectionService.java
+++ b/core/java/android/service/voice/HotwordDetectionService.java
@@ -16,6 +16,8 @@
 
 package android.service.voice;
 
+import static java.util.Objects.requireNonNull;
+
 import android.annotation.DurationMillisLong;
 import android.annotation.IntDef;
 import android.annotation.NonNull;
@@ -414,11 +416,15 @@ public abstract class HotwordDetectionService extends Service {
         }
 
         /**
-         * Called when the detected result is valid.
+         * Informs the {@link HotwordDetector} that the keyphrase was detected.
+         *
+         * @param result Info about the detection result. This is provided to the
+         *         {@link HotwordDetector}.
          */
-        public void onDetected(@Nullable HotwordDetectedResult hotwordDetectedResult) {
+        public void onDetected(@NonNull HotwordDetectedResult result) {
+            requireNonNull(result);
             try {
-                mRemoteCallback.onDetected(hotwordDetectedResult);
+                mRemoteCallback.onDetected(result);
             } catch (RemoteException e) {
                 throw e.rethrowFromSystemServer();
             }
@@ -433,7 +439,8 @@ public abstract class HotwordDetectionService extends Service {
          * @param result Info about the second stage detection result. This is provided to
          *         the {@link HotwordDetector}.
          */
-        public void onRejected(@Nullable HotwordRejectedResult result) {
+        public void onRejected(@NonNull HotwordRejectedResult result) {
+            requireNonNull(result);
             try {
                 mRemoteCallback.onRejected(result);
             } catch (RemoteException e) {
diff --git a/core/java/android/service/voice/HotwordDetector.java b/core/java/android/service/voice/HotwordDetector.java
index 2fb4dbc835edf..d3c10ea7c6708 100644
--- a/core/java/android/service/voice/HotwordDetector.java
+++ b/core/java/android/service/voice/HotwordDetector.java
@@ -160,7 +160,7 @@ public interface HotwordDetector {
          * @param result Info about the second stage detection result, provided by the
          *         {@link HotwordDetectionService}.
          */
-        void onRejected(@Nullable HotwordRejectedResult result);
+        void onRejected(@NonNull HotwordRejectedResult result);
 
         /**
          * Called when the {@link HotwordDetectionService} is created by the system and given a
diff --git a/services/voiceinteraction/java/com/android/server/voiceinteraction/HotwordDetectionConnection.java b/services/voiceinteraction/java/com/android/server/voiceinteraction/HotwordDetectionConnection.java
index d1bd159ee7ff5..5df3d9c0db655 100644
--- a/services/voiceinteraction/java/com/android/server/voiceinteraction/HotwordDetectionConnection.java
+++ b/services/voiceinteraction/java/com/android/server/voiceinteraction/HotwordDetectionConnection.java
@@ -612,7 +612,7 @@ final class HotwordDetectionConnection {
                         options,
                         new IDspHotwordDetectionCallback.Stub() {
                             @Override
-                            public void onRejected(@Nullable HotwordRejectedResult result)
+                            public void onRejected(HotwordRejectedResult result)
                                     throws RemoteException {
                                 bestEffortClose(serviceAudioSink);
                                 bestEffortClose(serviceAudioSource);
@@ -622,7 +622,7 @@ final class HotwordDetectionConnection {
                             }
 
                             @Override
-                            public void onDetected(@Nullable HotwordDetectedResult triggerResult)
+                            public void onDetected(HotwordDetectedResult triggerResult)
                                     throws RemoteException {
                                 bestEffortClose(serviceAudioSink);
                                 bestEffortClose(serviceAudioSource);