Ignore missing fields during rename

src/pythonjsonlogger/jsonlogger.py

@@ -229,8 +229,8 @@ def add_fields(
 
     def _perform_rename_log_fields(self, log_record):
         for old_field_name, new_field_name in self.rename_fields.items():
-            log_record[new_field_name] = log_record[old_field_name]
-            del log_record[old_field_name]
+            if old_field_name in log_record:
+                log_record[new_field_name] = log_record.pop(old_field_name)
 
     def process_log_record(self, log_record):
         """

tests/test_jsonlogger.py

@@ -56,21 +56,24 @@ def test_rename_base_field(self):
         fr = jsonlogger.JsonFormatter(rename_fields={'message': '@message'})
         self.log_handler.setFormatter(fr)
 
-        msg = "testing logging format"
+        msg = "testing logging rename"
         self.log.info(msg)
         log_json = json.loads(self.buffer.getvalue())
 
+        self.assertNotIn("message", log_json)
+        self.assertIn("@message", log_json)
         self.assertEqual(log_json["@message"], msg)
 
     def test_rename_nonexistent_field(self):
         fr = jsonlogger.JsonFormatter(rename_fields={'nonexistent_key': 'new_name'})
         self.log_handler.setFormatter(fr)
 
-        stderr_watcher = StringIO()
-        sys.stderr = stderr_watcher
-        self.log.info("testing logging rename")
+        msg = "testing logging rename"
+        self.log.info(msg)
+        log_json = json.loads(self.buffer.getvalue())
 
-        self.assertTrue("KeyError: 'nonexistent_key'" in stderr_watcher.getvalue())
+        self.assertNotIn("nonexistent_key", log_json)
+        self.assertNotIn("new_name", log_json)
 
     def test_add_static_fields(self):
         fr = jsonlogger.JsonFormatter(static_fields={'log_stream': 'kafka'})