Fix Android Fabric sync prop null override

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/fabric/mounting/SurfaceMountingManager.kt

@@ -672,6 +672,9 @@ internal constructor(
       modifiedProps.merge(props)
       val directPropsMap = checkNotNull(tagToSynchronousMountProps[reactTag])
       overridePropsReadableMap(directPropsMap, modifiedProps)
+      if (directPropsMap.isEmpty()) {
+        tagToSynchronousMountProps.remove(reactTag)
+      }
       viewState.currentProps = ReactStylesDiffMap(modifiedProps)
     } else {
       viewState.currentProps = ReactStylesDiffMap(props)
@@ -1326,11 +1329,18 @@ internal constructor(
     }
 
     private fun overridePropsReadableMap(
-        patchMap: Map<String, Any>,
+        patchMap: MutableMap<String, Any>,
         outputReadableMap: WritableMap,
     ) {
-      for ((propKey, propValue) in patchMap) {
+      val iterator = patchMap.entries.iterator()
+      while (iterator.hasNext()) {
+        val (propKey, propValue) = iterator.next()
         if (outputReadableMap.hasKey(propKey)) {
+          if (outputReadableMap.getType(propKey) == ReadableType.Null) {
+            iterator.remove()
+            continue
+          }
+
           if (propKey == PROP_TRANSFORM) {
             assert(outputReadableMap.getType(propKey) == ReadableType.Array && propValue is List<*>)
             val array = WritableNativeArray()

packages/react-native/ReactAndroid/src/test/java/com/facebook/react/fabric/SurfaceMountingManagerSynchronousMountPropsTest.kt

@@ -10,6 +10,7 @@
 package com.facebook.react.fabric
 
 import com.facebook.react.ReactRootView
+import com.facebook.react.bridge.JavaOnlyArray
 import com.facebook.react.bridge.JavaOnlyMap
 import com.facebook.react.bridge.ReactTestHelper
 import com.facebook.react.fabric.mounting.MountingManager
@@ -137,6 +138,39 @@ class SurfaceMountingManagerSynchronousMountPropsTest {
     assertThat(smm.getView(tag).alpha).isEqualTo(0.2f)
   }
 
+  /** A null Fabric prop update should clear the stored synchronous opacity override. */
+  @Test
+  fun updateProps_withNullOpacity_removesStoredSynchronousProp() {
+    val smm = startSurface()
+    val tag = 42
+    createAndAttachView(smm, tag)
+
+    smm.storeSynchronousMountPropsOverride(tag, JavaOnlyMap.of("opacity", 0.3))
+    smm.updatePropsSynchronously(tag, JavaOnlyMap.of("opacity", 0.3))
+    assertThat(smm.getView(tag).alpha).isEqualTo(0.3f)
+
+    smm.updateProps(tag, JavaOnlyMap.of("opacity", null))
+
+    assertThat(smm.getView(tag).alpha).isEqualTo(1.0f)
+  }
+
+  /** A null Fabric prop update should clear the stored synchronous transform override. */
+  @Test
+  fun updateProps_withNullTransform_removesStoredSynchronousProp() {
+    val smm = startSurface()
+    val tag = 42
+    val transform = JavaOnlyArray.of(JavaOnlyMap.of("translateY", 40.0))
+    createAndAttachView(smm, tag)
+
+    smm.storeSynchronousMountPropsOverride(tag, JavaOnlyMap.of("transform", transform))
+    smm.updatePropsSynchronously(tag, JavaOnlyMap.of("transform", transform))
+    assertThat(smm.getView(tag).translationY).isEqualTo(40.0f)
+
+    smm.updateProps(tag, JavaOnlyMap.of("transform", null))
+
+    assertThat(smm.getView(tag).translationY).isEqualTo(0.0f)
+  }
+
   /**
    * When a view is deleted, stored synchronous props should be cleaned up. A recreated view with
    * the same tag should not be affected by the old stored props.