fix: retain null field in sync node merger

src/main/java/com/aws/greengrass/shadowmanager/sync/model/FullShadowSyncRequest.java

@@ -172,13 +172,13 @@ && isDocVersionSame(localShadowDocument.get(), syncInformation, DataOwner.LOCAL)
         long cloudDocumentVersion = cloudShadowDocument.get().getVersion();
 
         // If the cloud document version is different from the last sync, that means the local document needed
-        // some updates. So we go ahead an update the local shadow document.
+        // some updates. So we go ahead and update the local shadow document.
         if (!isDocVersionSame(cloudShadowDocument.get(), syncInformation, DataOwner.CLOUD)) {
             localDocumentVersion = updateLocalDocumentAndGetUpdatedVersion(updateDocument,
                     Optional.of(localDocumentVersion));
         }
         // If the local document version is different from the last sync, that means the cloud document needed
-        // some updates. So we go ahead an update the cloud shadow document.
+        // some updates. So we go ahead and update the cloud shadow document.
         if (!isDocVersionSame(localShadowDocument.get(), syncInformation, DataOwner.LOCAL)) {
             cloudDocumentVersion = updateCloudDocumentAndGetUpdatedVersion(updateDocument,
                     Optional.of(cloudDocumentVersion));

src/main/java/com/aws/greengrass/shadowmanager/util/JsonMerger.java

@@ -26,7 +26,7 @@ private JsonMerger() {
 
     /**
      * Merges the patch JSON node to the existing source JSON node. If the node already exists in the source, then
-     * it replaces it. If the node is an array, then the the source array's contents are overwritten with the contents
+     * it replaces it. If the node is an array, then the source array's contents are overwritten with the contents
      * from the patch.
      *
      * @param source The source JSON to merge.
@@ -44,9 +44,6 @@ public static void merge(JsonNode source, final JsonNode patch) throws InvalidRe
             return;
         }
 
-        // If the source node contains keys not present in the patch node, those keys have been deleted
-        removeDeletedFields((ObjectNode) source, (ObjectNode) patch);
-
         // If both nodes are objects then do a recursive patch
         if (source.isObject() && patch.isObject()) {
             merge((ObjectNode) source, (ObjectNode) patch);
@@ -107,19 +104,6 @@ private static void merge(final ObjectNode source, final ObjectNode patch) {
         }
     }
 
-    private static void removeDeletedFields(final ObjectNode source, final ObjectNode patch) {
-        final Iterator<String> fieldNames = source.fieldNames();
-        while (fieldNames.hasNext()) {
-            final String field = fieldNames.next();
-            final JsonNode patchValue = patch.get(field);
-
-            // If the patch value is null then the field has been deleted, remove from source
-            if (isNullOrMissing(patchValue)) {
-                source.remove(field);
-            }
-        }
-    }
-
     /**
      * Creates a tree that can be merged into a JsonNode.  Does the following:
      * 1. removes nulls

src/main/java/com/aws/greengrass/shadowmanager/util/SyncNodeMerger.java

@@ -142,10 +142,11 @@ private static void iterateOverAllUnvisitedFields(JsonNode local, JsonNode cloud
             final JsonNode cloudValue = cloud.get(field);
             final JsonNode baseValue = base.get(field);
             JsonNode mergedResult = getMergedNode(localValue, cloudValue, baseValue, owner);
-            if (mergedResult != null) {
-                ((ObjectNode) result).set(field, mergedResult);
+            ((ObjectNode) result).set(field, mergedResult);
+            if (mergedResult == null) {
+                visited.add(field);
             }
-            visited.add(field);
+            //visited.add(field);
         }
     }