diff --git a/changes/2320-PrettyWood.md b/changes/2320-PrettyWood.md
new file mode 100644
index 0000000000..b3bd818aea
--- /dev/null
+++ b/changes/2320-PrettyWood.md
@@ -0,0 +1 @@
+fix: allow `None` for type `Optional[conset / conlist]`
diff --git a/pydantic/types.py b/pydantic/types.py
index 846e9ee310..1c2b2da838 100644
--- a/pydantic/types.py
+++ b/pydantic/types.py
@@ -106,7 +106,6 @@
 
 if TYPE_CHECKING:
     from .dataclasses import Dataclass  # noqa: F401
-    from .fields import ModelField
     from .main import BaseConfig, BaseModel  # noqa: F401
     from .typing import CallableGenerator
 
@@ -187,8 +186,8 @@ def __modify_schema__(cls, field_schema: Dict[str, Any]) -> None:
         update_not_none(field_schema, minItems=cls.min_items, maxItems=cls.max_items)
 
     @classmethod
-    def list_length_validator(cls, v: 'Optional[List[T]]', field: 'ModelField') -> 'Optional[List[T]]':
-        if v is None and not field.required:
+    def list_length_validator(cls, v: 'Optional[List[T]]') -> 'Optional[List[T]]':
+        if v is None:
             return None
 
         v = list_validator(v)
@@ -229,7 +228,10 @@ def __modify_schema__(cls, field_schema: Dict[str, Any]) -> None:
         update_not_none(field_schema, minItems=cls.min_items, maxItems=cls.max_items)
 
     @classmethod
-    def set_length_validator(cls, v: 'Optional[Set[T]]', field: 'ModelField') -> 'Optional[Set[T]]':
+    def set_length_validator(cls, v: 'Optional[Set[T]]') -> 'Optional[Set[T]]':
+        if v is None:
+            return None
+
         v = set_validator(v)
         v_len = len(v)
 
diff --git a/tests/test_types.py b/tests/test_types.py
index f019a7f5aa..66bb6b8627 100644
--- a/tests/test_types.py
+++ b/tests/test_types.py
@@ -172,6 +172,34 @@ class ConListModelMin(BaseModel):
     ]
 
 
+def test_constrained_list_optional():
+    class Model(BaseModel):
+        req: Optional[conlist(str, min_items=1)] = ...
+        opt: Optional[conlist(str, min_items=1)]
+
+    assert Model(req=None).dict() == {'req': None, 'opt': None}
+    assert Model(req=None, opt=None).dict() == {'req': None, 'opt': None}
+
+    with pytest.raises(ValidationError) as exc_info:
+        Model(req=[], opt=[])
+    assert exc_info.value.errors() == [
+        {
+            'loc': ('req',),
+            'msg': 'ensure this value has at least 1 items',
+            'type': 'value_error.list.min_items',
+            'ctx': {'limit_value': 1},
+        },
+        {
+            'loc': ('opt',),
+            'msg': 'ensure this value has at least 1 items',
+            'type': 'value_error.list.min_items',
+            'ctx': {'limit_value': 1},
+        },
+    ]
+
+    assert Model(req=['a'], opt=['a']).dict() == {'req': ['a'], 'opt': ['a']}
+
+
 def test_constrained_list_constraints():
     class ConListModelBoth(BaseModel):
         v: conlist(int, min_items=7, max_items=11)
@@ -323,6 +351,34 @@ class ConSetModelMin(BaseModel):
     ]
 
 
+def test_constrained_set_optional():
+    class Model(BaseModel):
+        req: Optional[conset(str, min_items=1)] = ...
+        opt: Optional[conset(str, min_items=1)]
+
+    assert Model(req=None).dict() == {'req': None, 'opt': None}
+    assert Model(req=None, opt=None).dict() == {'req': None, 'opt': None}
+
+    with pytest.raises(ValidationError) as exc_info:
+        Model(req=set(), opt=set())
+    assert exc_info.value.errors() == [
+        {
+            'loc': ('req',),
+            'msg': 'ensure this value has at least 1 items',
+            'type': 'value_error.set.min_items',
+            'ctx': {'limit_value': 1},
+        },
+        {
+            'loc': ('opt',),
+            'msg': 'ensure this value has at least 1 items',
+            'type': 'value_error.set.min_items',
+            'ctx': {'limit_value': 1},
+        },
+    ]
+
+    assert Model(req={'a'}, opt={'a'}).dict() == {'req': {'a'}, 'opt': {'a'}}
+
+
 def test_constrained_set_constraints():
     class ConSetModelBoth(BaseModel):
         v: conset(int, min_items=7, max_items=11)