Fix minor issues after introducing incremental JSON_PATCH merge

lib/Onyx.js

@@ -900,7 +900,7 @@ function set(key, value) {
     // This approach prioritizes fast UI changes without waiting for data to be stored in device storage.
     broadcastUpdate(key, value, hasChanged, 'set');
 
-    // If the value has not changed then we don't need to write it to storage
+    // If the value has not changed, calling Storage.setItem() would be redundant and a waste of performance, so return early instead.
     if (!hasChanged) {
         return Promise.resolve();
     }
@@ -961,7 +961,8 @@ function applyMerge(existingValue, changes) {
     if (_.isObject(existingValue) || _.every(changes, _.isObject)) {
         // Object values are merged one after the other
         // lodash adds a small overhead so we don't use it here
-        return _.reduce(changes, (modifiedData, change) => ({...fastMerge(modifiedData, change)}),
+        // eslint-disable-next-line prefer-object-spread, rulesdir/prefer-underscore-method
+        return _.reduce(changes, (modifiedData, change) => Object.assign({}, fastMerge(modifiedData, change)),
             existingValue || {});
     }
 
@@ -1012,7 +1013,8 @@ function merge(key, changes) {
                 // After that we merge the batched changes with the existing value
                 let modifiedData = applyMerge(existingValue, [batchedChanges]);
 
-                // For objects, we want to remove all top level keys that are null
+                // For objects, the key for null values needs to be removed from the object to ensure the value will get removed from storage completely.
+                // On native, SQLite will remove keys top-level keys that are null. To be consistent, we remove them on web too.
                 if (!_.isArray(modifiedData) && _.isObject(modifiedData)) {
                     modifiedData = _.omit(modifiedData, value => _.isNull(value));
                 }
@@ -1022,7 +1024,7 @@ function merge(key, changes) {
                 // This approach prioritizes fast UI changes without waiting for data to be stored in device storage.
                 broadcastUpdate(key, modifiedData, hasChanged, 'merge');
 
-                // If the value has not changed then we don't need to write it to storage
+                // If the value has not changed, calling Storage.setItem() would be redundant and a waste of performance, so return early instead.
                 if (!hasChanged) {
                     return Promise.resolve();
                 }