diff --git a/mkdocs/config/config_options.py b/mkdocs/config/config_options.py
index 3b4fa9ad..b76af0a7 100644
--- a/mkdocs/config/config_options.py
+++ b/mkdocs/config/config_options.py
@@ -394,14 +394,14 @@ class URL(OptionallyRequired[str]):
     """
 
     @overload
-    def __init__(self, default='', *, is_dir: bool = False):
+    def __init__(self, default=None, *, is_dir: bool = False):
         ...
 
     @overload
-    def __init__(self, default='', *, required: bool, is_dir: bool = False):
+    def __init__(self, default=None, *, required: bool, is_dir: bool = False):
         ...
 
-    def __init__(self, default='', required=None, is_dir: bool = False):
+    def __init__(self, default=None, required=None, is_dir: bool = False):
         self.is_dir = is_dir
         super().__init__(default, required=required)
 
diff --git a/mkdocs/tests/config/config_options_legacy_tests.py b/mkdocs/tests/config/config_options_legacy_tests.py
index 221ddb60..8a3d545b 100644
--- a/mkdocs/tests/config/config_options_legacy_tests.py
+++ b/mkdocs/tests/config/config_options_legacy_tests.py
@@ -432,9 +432,22 @@ class URLTest(TestCase):
         conf = self.get_config(Schema, {'option': "https://mkdocs.org"})
         self.assertEqual(conf['option'], "https://mkdocs.org/")
 
+    def test_optional(self):
+        class Schema:
+            option = c.URL(is_dir=True)
+
+        conf = self.get_config(Schema, {'option': ''})
+        self.assertEqual(conf['option'], '')
+
+        conf = self.get_config(Schema, {'option': None})
+        self.assertEqual(conf['option'], None)
+
     def test_invalid_url(self):
         class Schema:
-            option = c.URL()
+            option = c.URL(required=True)
+
+        with self.expect_error(option="Required configuration not provided."):
+            self.get_config(Schema, {'option': None})
 
         for url in "www.mkdocs.org", "//mkdocs.org/test", "http:/mkdocs.org/", "/hello/":
             with self.subTest(url=url):
diff --git a/mkdocs/tests/config/config_options_tests.py b/mkdocs/tests/config/config_options_tests.py
index 553dca6b..b64bf827 100644
--- a/mkdocs/tests/config/config_options_tests.py
+++ b/mkdocs/tests/config/config_options_tests.py
@@ -414,10 +414,23 @@ class URLTest(TestCase):
         conf = self.get_config(Schema, {'option': "https://mkdocs.org"})
         self.assertEqual(conf.option, "https://mkdocs.org/")
 
+    def test_optional(self):
+        class Schema(Config):
+            option = c.Optional(c.URL(is_dir=True))
+
+        conf = self.get_config(Schema, {'option': ''})
+        self.assertEqual(conf.option, '')
+
+        conf = self.get_config(Schema, {'option': None})
+        self.assertEqual(conf.option, None)
+
     def test_invalid_url(self) -> None:
         class Schema(Config):
             option = c.URL()
 
+        with self.expect_error(option="Required configuration not provided."):
+            self.get_config(Schema, {'option': None})
+
         for url in "www.mkdocs.org", "//mkdocs.org/test", "http:/mkdocs.org/", "/hello/":
             with self.subTest(url=url):
                 with self.expect_error(