[python-package] simplify Dataset._compare_params_for_warning() (#6120)

python-package/lightgbm/basic.py

@@ -2200,8 +2200,8 @@ class Dataset:
 
     @staticmethod
     def _compare_params_for_warning(
-        params: Optional[Dict[str, Any]],
-        other_params: Optional[Dict[str, Any]],
+        params: Dict[str, Any],
+        other_params: Dict[str, Any],
         ignore_keys: Set[str]
     ) -> bool:
         """Compare two dictionaries with params ignoring some keys.
@@ -2210,9 +2210,9 @@ class Dataset:
 
         Parameters
         ----------
-        params : dict or None
+        params : dict
             One dictionary with parameters to compare.
-        other_params : dict or None
+        other_params : dict
             Another dictionary with parameters to compare.
         ignore_keys : set
             Keys that should be ignored during comparing two dictionaries.
@@ -2222,10 +2222,6 @@ class Dataset:
         compare_result : bool
           Returns whether two dictionaries with params are equal.
         """
-        if params is None:
-            params = {}
-        if other_params is None:
-            other_params = {}
         for k in other_params:
             if k not in ignore_keys:
                 if k not in params or params[k] != other_params[k]: