Allow None in _validate_meta parameter validation

Update _validate_meta function to accept None as a valid input.

Author: nocoding03

pandas/io/json/_normalize.py

@@ -267,20 +267,20 @@ def _simple_json_normalize(
     return normalized_json_object
 
 
-def _validate_meta(meta: str | list[str | list[str]]) -> None:
+def _validate_meta(meta: str | list[str | list[str]] | None) -> None:
     """
     Validate that meta parameter contains only strings or lists of strings.
-
     Parameters
     ----------
-    meta : str or list of str or list of list of str
+    meta : str or list of str or list of list of str or None
         The meta parameter to validate.
-
     Raises
     ------
     TypeError
         If meta contains elements that are not strings or lists of strings.
     """
+    if meta is None:
+        return
     if isinstance(meta, str):
         return
     for item in meta:
@@ -468,8 +468,7 @@ def json_normalize(
 
     Returns normalized data with columns prefixed with the given string.
     """
-    if meta is not None:
-        _validate_meta(meta)
+    _validate_meta(meta)
 
     def _pull_field(
         js: dict[str, Any], spec: list | str, extract_record: bool = False