Update elements.py

Author: Conengmo

folium/elements.py

@@ -9,7 +9,7 @@ class JSCSSMixin(Element):
     default_js: List[Tuple[str, str]] = []
     default_css: List[Tuple[str, str]] = []
 
-    def render(self, **kwargs):
+    def render(self, **kwargs) -> None:
         figure = self.get_root()
         assert isinstance(
             figure, Figure