fix(storage): correctly insert explicit nulls for json patch updates (#13716)

Fix integration test issue in JSON Patch Updates

Co-authored-by: Dhriti Chopra <dhritichopra@google.com>

Author: Dhriti07

java-storage/google-cloud-storage/src/main/java/com/google/cloud/storage/StorageImpl.java

@@ -492,8 +492,9 @@ public Bucket update(BucketInfo bucketInfo, BucketTargetOption... options) {
           .forEach(
               field -> {
                 String jsonName = field.getApiaryName();
-                if (tmp.containsKey(jsonName)) {
-                  bucketPb.put(jsonName, tmp.get(jsonName));
+                Object value = tmp.get(jsonName);
+                if (value != null) {
+                  bucketPb.put(jsonName, value);
                 } else {
                   BucketField lookup = BucketField.lookup(field);
                   if (lookup != null) {
@@ -577,8 +578,9 @@ public Blob update(BlobInfo blobInfo, BlobTargetOption... options) {
             } else {
               checkState(subFields.size() <= 1, "unexpected nested field(s) %s", subFields);
               String jsonName = topLevelField.getApiaryName();
-              if (tmp.containsKey(jsonName)) {
-                pb.put(jsonName, tmp.get(jsonName));
+              Object value = tmp.get(jsonName);
+              if (value != null) {
+                pb.put(jsonName, value);
               } else {
                 BlobField lookup = BlobField.lookup(topLevelField);
                 if (lookup != null) {