minor optimize

Signed-off-by: luofucong <luofc@foxmail.com>

src/datatypes/src/json/value.rs

@@ -427,8 +427,7 @@ impl JsonValue {
     /// - `Null` aligns to any type, and any value aligns to `Null` as `Null`.
     /// - Numbers are converted only within compatible number categories.
     /// - Arrays align each element recursively to the expected item type.
-    /// - Objects require `expected` to contain all fields from the current value. Missing expected
-    ///   fields are filled with `Null`.
+    /// - Objects require `expected` to have all fields from the current value.
     /// - `Variant` preserves the original JSON payload as serialized bytes.
     ///
     /// Returns an error if the value cannot be aligned without losing existing object fields or
@@ -467,7 +466,6 @@ impl JsonValue {
                         .collect::<Result<_>>()?,
                 ),
 
-                (JsonVariant::Object(kvs), _) if kvs.is_empty() => JsonVariant::Null,
                 (JsonVariant::Object(mut kvs), JsonNativeType::Object(expected)) => {
                     ensure!(
                         expected.keys().len() >= kvs.keys().len()
@@ -481,15 +479,12 @@ impl JsonValue {
                         }
                     );
 
-                    let mut object = BTreeMap::new();
                     for (field, field_type) in expected {
                         if let Some((k, v)) = kvs.remove_entry(field) {
-                            object.insert(k, helper(v, field_type)?);
-                        } else {
-                            object.insert(field.clone(), JsonVariant::Null);
+                            kvs.insert(k, helper(v, field_type)?);
                         }
                     }
-                    JsonVariant::Object(object)
+                    JsonVariant::Object(kvs)
                 }
 
                 (v, JsonNativeType::Variant) => {

src/datatypes/src/vectors/json/builder.rs

@@ -62,10 +62,6 @@ impl JsonVectorBuilder {
                 continue;
             }
             value.try_align(&self.merged_type)?;
-            if value.is_null() {
-                builder.push_null();
-                continue;
-            }
             let value_ref = json_variant_to_struct_value_ref(value.variant(), struct_type.clone())?;
             builder.push_struct_value_ref(value_ref)?;
         }