fix(differ): improve array item handling in schema comparison

- Ensure proper handling of array items in the schema comparison module.
- Update logic to check for None values and provide clearer output for empty items.
- Adjust item field summaries to include a count of additional fields when more than five are present.

Author: halilibrahimd27

schema-monitor/core/differ.py

@@ -70,15 +70,18 @@ def _field_summary(field_data: dict[str, Any]) -> str:
 
     if field_type == "array" and "items" in field_data:
         items = field_data["items"]
-        items_type = items.get("type", "unknown")
-        if items_type == "object" and "fields" in items:
-            item_fields = list(items["fields"].keys())
-            if len(item_fields) <= 5:
-                parts.append(f"items: {items_type} [{', '.join(item_fields)}]")
+        if items is not None:
+            items_type = items.get("type", "unknown")
+            if items_type == "object" and "fields" in items:
+                item_fields = list(items["fields"].keys())
+                if len(item_fields) <= 5:
+                    parts.append(f"items: {items_type} [{', '.join(item_fields)}]")
+                else:
+                    parts.append(f"items: {items_type} [{', '.join(item_fields[:5])}, ... +{len(item_fields) - 5}]")
             else:
-                parts.append(f"items: {items_type} [{', '.join(item_fields[:5])}, ... +{len(item_fields) - 5}]")
+                parts.append(f"items: {items_type}")
         else:
-            parts.append(f"items: {items_type}")
+            parts.append("items: empty")
 
     if "sample" in field_data:
         sample = str(field_data["sample"])
@@ -116,13 +119,16 @@ def _field_to_json_preview(field_data: dict[str, Any], max_depth: int = 2) -> di
 
         if field_data.get("type") == "array" and "items" in field_data:
             items = field_data["items"]
-            if items.get("type") == "object" and "fields" in items:
-                sub_fields = {}
-                for name, sub_data in items["fields"].items():
-                    sub_fields[name] = sub_data.get("type", "unknown")
-                result["items"] = {"type": "object", "fields": sub_fields}
+            if items is not None:
+                if items.get("type") == "object" and "fields" in items:
+                    sub_fields = {}
+                    for name, sub_data in items["fields"].items():
+                        sub_fields[name] = sub_data.get("type", "unknown")
+                    result["items"] = {"type": "object", "fields": sub_fields}
+                else:
+                    result["items"] = {"type": items.get("type", "unknown")}
             else:
-                result["items"] = {"type": items.get("type", "unknown")}
+                result["items"] = {"type": "empty"}
 
     return result