Fix null pointer exception (#2761)

* Fix  npe for copyNecessaryFilesFromCurrentPackage

* Reformat code

Author: DordeDimitrijev

android/app/src/main/java/com/microsoft/codepush/react/CodePushUpdateUtils.java

@@ -9,7 +9,6 @@
 
 import java.security.interfaces.*;
 
-
 import org.json.JSONArray;
 import org.json.JSONException;
 import org.json.JSONObject;
@@ -86,8 +85,12 @@ private static String computeHash(InputStream dataStream) {
             throw new CodePushUnknownException("Unable to compute hash of update contents.", e);
         } finally {
             try {
-                if (digestInputStream != null) digestInputStream.close();
-                if (dataStream != null) dataStream.close();
+                if (digestInputStream != null) {
+                    digestInputStream.close();
+                }
+                if (dataStream != null) {
+                    dataStream.close();
+                }
             } catch (IOException e) {
                 e.printStackTrace();
             }
@@ -98,7 +101,11 @@ private static String computeHash(InputStream dataStream) {
     }
 
     public static void copyNecessaryFilesFromCurrentPackage(String diffManifestFilePath, String currentPackageFolderPath, String newPackageFolderPath) throws IOException {
-        FileUtils.copyDirectoryContents(currentPackageFolderPath, newPackageFolderPath);        
+        if (currentPackageFolderPath == null || !new File(currentPackageFolderPath).exists()) {
+            CodePushUtils.log("Unable to copy files from current package during diff update, because currentPackageFolderPath is invalid.");
+            return;
+        }
+        FileUtils.copyDirectoryContents(currentPackageFolderPath, newPackageFolderPath);
         JSONObject diffManifest = CodePushUtils.getJsonObjectFromFile(diffManifestFilePath);
         try {
             JSONArray deletedFiles = diffManifest.getJSONArray("deletedFiles");
@@ -184,7 +191,7 @@ public static void verifyFolderHash(String folderPath, String expectedHash) {
     public static Map<String, Object> verifyAndDecodeJWT(String jwt, PublicKey publicKey) {
         try {
             SignedJWT signedJWT = SignedJWT.parse(jwt);
-            JWSVerifier verifier = new RSASSAVerifier((RSAPublicKey)publicKey);
+            JWSVerifier verifier = new RSASSAVerifier((RSAPublicKey) publicKey);
             if (signedJWT.verify(verifier)) {
                 Map<String, Object> claims = signedJWT.getJWTClaimsSet().getClaims();
                 CodePushUtils.log("JWT verification succeeded, payload content: " + claims.toString());
@@ -217,7 +224,7 @@ public static PublicKey parsePublicKey(String stringPublicKey) {
         }
     }
 
-    public static String getSignatureFilePath(String updateFolderPath){
+    public static String getSignatureFilePath(String updateFolderPath) {
         return CodePushUtils.appendPathComponent(
                 CodePushUtils.appendPathComponent(updateFolderPath, CodePushConstants.CODE_PUSH_FOLDER_PREFIX),
                 CodePushConstants.BUNDLE_JWT_FILE
@@ -254,7 +261,7 @@ public static void verifyUpdateSignature(String folderPath, String packageHash,
             throw new CodePushInvalidUpdateException("The update could not be verified because it was not signed by a trusted party.");
         }
 
-        final String contentHash = (String)claims.get("contentHash");
+        final String contentHash = (String) claims.get("contentHash");
         if (contentHash == null) {
             throw new CodePushInvalidUpdateException("The update could not be verified because the signature did not specify a content hash.");
         }
@@ -265,4 +272,4 @@ public static void verifyUpdateSignature(String folderPath, String packageHash,
 
         CodePushUtils.log("The update contents succeeded the code signing check.");
     }
-}
+}