[camera_android] Mark description in sendCameraErrorEvent as `@No…

…nNull` (#7877)

`sendCameraErrorEvent` is package-visible and only called in
`Camera.java` and `CameraTest.java`. This should be test- and
version-exempt, as it is essentially just an annotation change.

Fixes flutter/flutter#156729

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packages/camera/camera_android/android/src/main/java/io/flutter/plugins/camera/Camera.java

@@ -396,10 +396,14 @@ public void onOpened(@NonNull CameraDevice device) {
                     cameraFeatures.getFocusPoint().checkIsSupported());
               }
             } catch (Exception e) {
+              String message =
+                  (e.getMessage() == null)
+                      ? (e.getClass().getName() + " occurred while opening camera.")
+                      : e.getMessage();
               if (BuildConfig.DEBUG) {
-                Log.i(TAG, "open | onOpened error: " + e.getMessage());
+                Log.i(TAG, "open | onOpened error: " + message);
               }
-              dartMessenger.sendCameraErrorEvent(e.getMessage());
+              dartMessenger.sendCameraErrorEvent(message);
               close();
             }
           }
@@ -792,7 +796,11 @@ private void lockAutoFocus() {
     try {
       captureSession.capture(previewRequestBuilder.build(), null, backgroundHandler);
     } catch (CameraAccessException e) {
-      dartMessenger.sendCameraErrorEvent(e.getMessage());
+      String message =
+          (e.getMessage() == null)
+              ? "CameraAccessException occurred while locking autofocus."
+              : e.getMessage();
+      dartMessenger.sendCameraErrorEvent(message);
     }
   }
 
@@ -815,7 +823,11 @@ void unlockAutoFocus() {
 
       captureSession.capture(previewRequestBuilder.build(), null, backgroundHandler);
     } catch (CameraAccessException e) {
-      dartMessenger.sendCameraErrorEvent(e.getMessage());
+      String message =
+          (e.getMessage() == null)
+              ? "CameraAccessException occurred while unlocking autofocus."
+              : e.getMessage();
+      dartMessenger.sendCameraErrorEvent(message);
       return;
     }
 

packages/camera/camera_android/android/src/main/java/io/flutter/plugins/camera/DartMessenger.java

@@ -95,17 +95,14 @@ void sendCameraClosingEvent() {
     handler.post(() -> eventApi.closed(new NoOpVoidResult()));
   }
 
-  // TODO(schectman): Make `description` non-null, see
-  // https://github.com/flutter/flutter/issues/156729
   /**
    * Sends a message to the Flutter client informing that an error occurred while interacting with
    * the camera.
    *
    * @param description contains details regarding the error that occurred.
    */
-  void sendCameraErrorEvent(@Nullable String description) {
-    String errorMessage = (description == null) ? "" : description;
-    handler.post(() -> eventApi.error(errorMessage, new NoOpVoidResult()));
+  void sendCameraErrorEvent(@NonNull String description) {
+    handler.post(() -> eventApi.error(description, new NoOpVoidResult()));
   }
 
   /**