fix nullsafe FIXMES for DynamicFromObject.java and mark nullsafe

Summary:
Gone trough all the FIXMEs added in the previous diff by the nullsafe tool, marked the class as nullsafe and ensured no remaining violations.
Changelog: [Android][Fixed] Made DynamicFromObject.java nullsafe

Reviewed By: alanleedev

Differential Revision: D72384066

fbshipit-source-id: 6f187f8a87a2c5d239c671880404eb81f0e22d3e

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/bridge/DynamicFromObject.java

@@ -9,9 +9,11 @@ package com.facebook.react.bridge;
 
 import androidx.annotation.Nullable;
 import com.facebook.common.logging.FLog;
+import com.facebook.infer.annotation.Nullsafe;
 import com.facebook.react.common.ReactConstants;
 
 /** Implementation of Dynamic wrapping a ReadableArray. */
+@Nullsafe(Nullsafe.Mode.LOCAL)
 public class DynamicFromObject implements Dynamic {
   private @Nullable Object mObject;
 
@@ -31,38 +33,50 @@ public class DynamicFromObject implements Dynamic {
 
   @Override
   public boolean asBoolean() {
-    // NULLSAFE_FIXME[Nullable Dereference]
+    if (mObject == null || !(mObject instanceof Boolean)) {
+      throw new ClassCastException("Dynamic value from Object is not a boolean");
+    }
     return (boolean) mObject;
   }
 
   @Override
   public double asDouble() {
-    // NULLSAFE_FIXME[Nullable Dereference]
+    if (mObject == null || !(mObject instanceof Number)) {
+      throw new ClassCastException("Dynamic value from Object is not a number");
+    }
     return (double) mObject;
   }
 
   @Override
   public int asInt() {
+    if (mObject == null || !(mObject instanceof Number)) {
+      throw new ClassCastException("Dynamic value from Object is not a number");
+    }
     // Numbers from JS are always Doubles
-    // NULLSAFE_FIXME[Nullable Dereference]
     return ((Double) mObject).intValue();
   }
 
   @Override
   public String asString() {
-    // NULLSAFE_FIXME[Return Not Nullable]
+    if (mObject == null || !(mObject instanceof String)) {
+      throw new ClassCastException("Dynamic value from Object is not a string");
+    }
     return (String) mObject;
   }
 
   @Override
   public ReadableArray asArray() {
-    // NULLSAFE_FIXME[Return Not Nullable]
+    if (mObject == null || !(mObject instanceof ReadableArray)) {
+      throw new ClassCastException("Dynamic value from Object is not a ReadableArray");
+    }
     return (ReadableArray) mObject;
   }
 
   @Override
   public ReadableMap asMap() {
-    // NULLSAFE_FIXME[Return Not Nullable]
+    if (mObject == null || !(mObject instanceof ReadableMap)) {
+      throw new ClassCastException("Dynamic value from Object is not a ReadableMap");
+    }
     return (ReadableMap) mObject;
   }