diff --git a/tests/test_request_params/test_body/test_nullable_and_defaults.py b/tests/test_request_params/test_body/test_nullable_and_defaults.py
index 0e032e8419..7696f765fd 100644
--- a/tests/test_request_params/test_body/test_nullable_and_defaults.py
+++ b/tests/test_request_params/test_body/test_nullable_and_defaults.py
@@ -1,25 +1,34 @@
 from typing import Annotated, Any, Union
+from unittest.mock import Mock, patch
 
 import pytest
 from dirty_equals import IsList, IsOneOf
 from fastapi import Body, FastAPI
 from fastapi.testclient import TestClient
-from pydantic import BaseModel
+from pydantic import BaseModel, BeforeValidator, field_validator
 
 from .utils import get_body_model_name
 
 app = FastAPI()
 
 
+def convert(v: Any) -> Any:
+    return v
+
+
 # =====================================================================================
 # Nullable required
 
 
 @app.post("/nullable-required")
 async def read_nullable_required(
-    int_val: Annotated[Union[int, None], Body()],
-    str_val: Annotated[Union[str, None], Body()],
-    list_val: Union[list[int], None],
+    int_val: Annotated[Union[int, None], Body(), BeforeValidator(lambda v: convert(v))],
+    str_val: Annotated[Union[str, None], Body(), BeforeValidator(lambda v: convert(v))],
+    list_val: Annotated[
+        Union[list[int], None],
+        Body(),
+        BeforeValidator(lambda v: convert(v)),
+    ],
 ):
     return {
         "int_val": int_val,
@@ -34,6 +43,10 @@ class ModelNullableRequired(BaseModel):
     str_val: Union[str, None]
     list_val: Union[list[int], None]
 
+    @field_validator("*", mode="before")
+    def validate_all(cls, v):
+        return convert(v)
+
 
 @app.post("/model-nullable-required")
 async def read_model_nullable_required(params: ModelNullableRequired):
@@ -47,21 +60,23 @@ async def read_model_nullable_required(params: ModelNullableRequired):
 
 @app.post("/nullable-required-str")
 async def read_nullable_required_no_embed_str(
-    str_val: Annotated[Union[str, None], Body()],
+    str_val: Annotated[Union[str, None], Body(), BeforeValidator(lambda v: convert(v))],
 ):
     return {"val": str_val}
 
 
 @app.post("/nullable-required-int")
 async def read_nullable_required_no_embed_int(
-    int_val: Annotated[Union[int, None], Body()],
+    int_val: Annotated[Union[int, None], Body(), BeforeValidator(lambda v: convert(v))],
 ):
     return {"val": int_val}
 
 
 @app.post("/nullable-required-list")
 async def read_nullable_required_no_embed_list(
-    list_val: Annotated[Union[list[int], None], Body()],
+    list_val: Annotated[
+        Union[list[int], None], Body(), BeforeValidator(lambda v: convert(v))
+    ],
 ):
     return {"val": list_val}
 
@@ -278,14 +293,18 @@ def test_nullable_required_pass_empty_dict(path: str, msg: str, error_type: str)
 )
 def test_nullable_required_pass_null(path: str):
     client = TestClient(app)
-    response = client.post(
-        path,
-        json={
-            "int_val": None,
-            "str_val": None,
-            "list_val": None,
-        },
-    )
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.post(
+            path,
+            json={
+                "int_val": None,
+                "str_val": None,
+                "list_val": None,
+            },
+        )
+
+    assert mock_convert.call_count == 3, "Validator should be called for each field"
     assert response.status_code == 200, response.text
     assert response.json() == {
         "int_val": None,
@@ -308,10 +327,13 @@ def test_nullable_required_pass_null(path: str):
 @pytest.mark.xfail(reason="Explicit null-body is treated as missing")
 def test_nullable_required_no_embed_pass_null(path: str):
     client = TestClient(app)
-    response = client.post(path, content="null")
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.post(path, content="null")
+
+    assert mock_convert.call_count == 1, "Validator should be called once for the field"
     assert response.status_code == 200, response.text
     assert response.json() == {"val": None}
-    # TODO: add test with BeforeValidator to ensure that it recieves `None` value
 
 
 @pytest.mark.parametrize(
@@ -323,9 +345,13 @@ def test_nullable_required_no_embed_pass_null(path: str):
 )
 def test_nullable_required_pass_value(path: str):
     client = TestClient(app)
-    response = client.post(
-        path, json={"int_val": "1", "str_val": "test", "list_val": ["1", "2"]}
-    )
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.post(
+            path, json={"int_val": "1", "str_val": "test", "list_val": ["1", "2"]}
+        )
+
+    assert mock_convert.call_count == 3, "Validator should be called for each field"
     assert response.status_code == 200, response.text
     assert response.json() == {
         "int_val": 1,
@@ -347,10 +373,11 @@ def test_nullable_required_pass_value(path: str):
 )
 def test_nullable_required_no_embed_pass_value(path: str, value: Any):
     client = TestClient(app)
-    response = client.post(
-        path,
-        json=value,
-    )
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.post(path, json=value)
+
+    assert mock_convert.call_count == 1, "Validator should be called once for the field"
     assert response.status_code == 200, response.text
     assert response.json() == {"val": value}
 
@@ -361,9 +388,21 @@ def test_nullable_required_no_embed_pass_value(path: str, value: Any):
 
 @app.post("/nullable-non-required")
 async def read_nullable_non_required(
-    int_val: Annotated[Union[int, None], Body()] = None,
-    str_val: Annotated[Union[str, None], Body()] = None,
-    list_val: Union[list[int], None] = None,
+    int_val: Annotated[
+        Union[int, None],
+        Body(),
+        BeforeValidator(lambda v: convert(v)),
+    ] = None,
+    str_val: Annotated[
+        Union[str, None],
+        Body(),
+        BeforeValidator(lambda v: convert(v)),
+    ] = None,
+    list_val: Annotated[
+        Union[list[int], None],
+        Body(),
+        BeforeValidator(lambda v: convert(v)),
+    ] = None,
 ):
     return {
         "int_val": int_val,
@@ -378,6 +417,10 @@ class ModelNullableNonRequired(BaseModel):
     str_val: Union[str, None] = None
     list_val: Union[list[int], None] = None
 
+    @field_validator("*", mode="before")
+    def validate_all(cls, v):
+        return convert(v)
+
 
 @app.post("/model-nullable-non-required")
 async def read_model_nullable_non_required(
@@ -393,21 +436,33 @@ async def read_model_nullable_non_required(
 
 @app.post("/nullable-non-required-str")
 async def read_nullable_non_required_no_embed_str(
-    str_val: Annotated[Union[str, None], Body()] = None,
+    str_val: Annotated[
+        Union[str, None],
+        Body(),
+        BeforeValidator(lambda v: convert(v)),
+    ] = None,
 ):
     return {"val": str_val}
 
 
 @app.post("/nullable-non-required-int")
 async def read_nullable_non_required_no_embed_int(
-    int_val: Annotated[Union[int, None], Body()] = None,
+    int_val: Annotated[
+        Union[int, None],
+        Body(),
+        BeforeValidator(lambda v: convert(v)),
+    ] = None,
 ):
     return {"val": int_val}
 
 
 @app.post("/nullable-non-required-list")
 async def read_nullable_non_required_no_embed_list(
-    list_val: Annotated[Union[list[int], None], Body()] = None,
+    list_val: Annotated[
+        Union[list[int], None],
+        Body(),
+        BeforeValidator(lambda v: convert(v)),
+    ] = None,
 ):
     return {"val": list_val}
 
@@ -499,7 +554,13 @@ def test_nullable_non_required_no_embed_schema(path: str, schema: dict):
 )
 def test_nullable_non_required_missing(path: str):
     client = TestClient(app)
-    response = client.post(path, json={})
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.post(path, json={})
+
+    assert mock_convert.call_count == 0, (
+        "Validator should not be called if the value is missing"
+    )
     assert response.status_code == 200
     assert response.json() == {
         "int_val": None,
@@ -547,7 +608,13 @@ def test_nullable_non_required_no_body(path: str):
 )
 def test_nullable_non_required_no_embed_missing(path: str):
     client = TestClient(app)
-    response = client.post(path)
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.post(path)
+
+    assert mock_convert.call_count == 0, (
+        "Validator should not be called if the value is missing"
+    )
     assert response.status_code == 200
     assert response.json() == {"val": None}
 
@@ -555,20 +622,29 @@ def test_nullable_non_required_no_embed_missing(path: str):
 @pytest.mark.parametrize(
     "path",
     [
-        "/nullable-non-required",
+        pytest.param(
+            "/nullable-non-required",
+            marks=pytest.mark.xfail(
+                reason="Null values are treated as missing for non-model Body parameters"
+            ),
+        ),
         "/model-nullable-non-required",
     ],
 )
 def test_nullable_non_required_pass_null(path: str):
     client = TestClient(app)
-    response = client.post(
-        path,
-        json={
-            "int_val": None,
-            "str_val": None,
-            "list_val": None,
-        },
-    )
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.post(
+            path,
+            json={
+                "int_val": None,
+                "str_val": None,
+                "list_val": None,
+            },
+        )
+
+    assert mock_convert.call_count == 3, "Validator should be called for each field"
     assert response.status_code == 200, response.text
     assert response.json() == {
         "int_val": None,
@@ -588,12 +664,16 @@ def test_nullable_non_required_pass_null(path: str):
         "/nullable-non-required-list",
     ],
 )
+@pytest.mark.xfail(reason="Explicit null-body is treated as missing")
 def test_nullable_non_required_no_embed_pass_null(path: str):
     client = TestClient(app)
-    response = client.post(path, content="null")
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.post(path, content="null")
+
+    assert mock_convert.call_count == 1, "Validator should be called once for the field"
     assert response.status_code == 200, response.text
     assert response.json() == {"val": None}
-    # TODO: add test with BeforeValidator to ensure that it recieves `None` value
 
 
 @pytest.mark.parametrize(
@@ -605,9 +685,13 @@ def test_nullable_non_required_no_embed_pass_null(path: str):
 )
 def test_nullable_non_required_pass_value(path: str):
     client = TestClient(app)
-    response = client.post(
-        path, json={"int_val": 1, "str_val": "test", "list_val": [1, 2]}
-    )
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.post(
+            path, json={"int_val": 1, "str_val": "test", "list_val": [1, 2]}
+        )
+
+    assert mock_convert.call_count == 3, "Validator should be called for each field"
     assert response.status_code == 200, response.text
     assert response.json() == {
         "int_val": 1,
@@ -629,7 +713,11 @@ def test_nullable_non_required_pass_value(path: str):
 )
 def test_nullable_non_required_no_embed_pass_value(path: str, value: Any):
     client = TestClient(app)
-    response = client.post(path, json=value)
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.post(path, json=value)
+
+    assert mock_convert.call_count == 1, "Validator should be called once for the field"
     assert response.status_code == 200, response.text
     assert response.json() == {"val": value}
 
@@ -641,9 +729,21 @@ def test_nullable_non_required_no_embed_pass_value(path: str, value: Any):
 @app.post("/nullable-with-non-null-default")
 async def read_nullable_with_non_null_default(
     *,
-    int_val: Annotated[Union[int, None], Body()] = -1,
-    str_val: Annotated[Union[str, None], Body()] = "default",
-    list_val: Annotated[Union[list[int], None], Body(default_factory=lambda: [0])],
+    int_val: Annotated[
+        Union[int, None],
+        Body(),
+        BeforeValidator(lambda v: convert(v)),
+    ] = -1,
+    str_val: Annotated[
+        Union[str, None],
+        Body(),
+        BeforeValidator(lambda v: convert(v)),
+    ] = "default",
+    list_val: Annotated[
+        Union[list[int], None],
+        Body(default_factory=lambda: [0]),
+        BeforeValidator(lambda v: convert(v)),
+    ],
 ):
     return {
         "int_val": int_val,
@@ -658,6 +758,10 @@ class ModelNullableWithNonNullDefault(BaseModel):
     str_val: Union[str, None] = "default"
     list_val: Union[list[int], None] = [0]
 
+    @field_validator("*", mode="before")
+    def validate_all(cls, v):
+        return convert(v)
+
 
 @app.post("/model-nullable-with-non-null-default")
 async def read_model_nullable_with_non_null_default(
@@ -673,21 +777,33 @@ async def read_model_nullable_with_non_null_default(
 
 @app.post("/nullable-with-non-null-default-str")
 async def read_nullable_with_non_null_default_no_embed_str(
-    str_val: Annotated[Union[str, None], Body()] = "default",
+    str_val: Annotated[
+        Union[str, None],
+        Body(),
+        BeforeValidator(lambda v: convert(v)),
+    ] = "default",
 ):
     return {"val": str_val}
 
 
 @app.post("/nullable-with-non-null-default-int")
 async def read_nullable_with_non_null_default_no_embed_int(
-    int_val: Annotated[Union[int, None], Body()] = -1,
+    int_val: Annotated[
+        Union[int, None],
+        Body(),
+        BeforeValidator(lambda v: convert(v)),
+    ] = -1,
 ):
     return {"val": int_val}
 
 
 @app.post("/nullable-with-non-null-default-list")
 async def read_nullable_with_non_null_default_no_embed_list(
-    list_val: Annotated[Union[list[int], None], Body(default_factory=lambda: [0])],
+    list_val: Annotated[
+        Union[list[int], None],
+        Body(default_factory=lambda: [0]),
+        BeforeValidator(lambda v: convert(v)),
+    ],
 ):
     return {"val": list_val}
 
@@ -787,7 +903,13 @@ def test_nullable_with_non_null_default_no_embed_schema(path: str, schema: dict)
 )
 def test_nullable_with_non_null_default_missing(path: str):
     client = TestClient(app)
-    response = client.post(path, json={})
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.post(path, json={})
+
+    assert mock_convert.call_count == 0, (
+        "Validator should not be called if the value is missing"
+    )
     assert response.status_code == 200, response.text
     assert response.json() == {
         "int_val": -1,
@@ -835,7 +957,13 @@ def test_nullable_with_non_null_default_no_body(path: str):
 )
 def test_nullable_with_non_null_default_no_embed_missing(path: str, expected: Any):
     client = TestClient(app)
-    response = client.post(path)
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.post(path)
+
+    assert mock_convert.call_count == 0, (
+        "Validator should not be called if the value is missing"
+    )
     assert response.status_code == 200, response.text
     assert response.json() == {"val": expected}
 
@@ -854,14 +982,18 @@ def test_nullable_with_non_null_default_no_embed_missing(path: str, expected: An
 )
 def test_nullable_with_non_null_default_pass_null(path: str):
     client = TestClient(app)
-    response = client.post(
-        path,
-        json={
-            "int_val": None,
-            "str_val": None,
-            "list_val": None,
-        },
-    )
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.post(
+            path,
+            json={
+                "int_val": None,
+                "str_val": None,
+                "list_val": None,
+            },
+        )
+
+    assert mock_convert.call_count == 3, "Validator should be called for each field"
     assert response.status_code == 200, response.text
     assert response.json() == {
         "int_val": None,
@@ -884,7 +1016,11 @@ def test_nullable_with_non_null_default_pass_null(path: str):
 @pytest.mark.xfail(reason="Explicit null-body is treated as missing")
 def test_nullable_with_non_null_default_no_embed_pass_null(path: str):
     client = TestClient(app)
-    response = client.post(path, content="null")
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.post(path, content="null")
+
+    assert mock_convert.call_count == 1, "Validator should be called once for the field"
     assert response.status_code == 200, response.text
     assert response.json() == {"val": None}
 
@@ -898,9 +1034,13 @@ def test_nullable_with_non_null_default_no_embed_pass_null(path: str):
 )
 def test_nullable_with_non_null_default_pass_value(path: str):
     client = TestClient(app)
-    response = client.post(
-        path, json={"int_val": "1", "str_val": "test", "list_val": ["1", "2"]}
-    )
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.post(
+            path, json={"int_val": "1", "str_val": "test", "list_val": ["1", "2"]}
+        )
+
+    assert mock_convert.call_count == 3, "Validator should be called for each field"
     assert response.status_code == 200, response.text
     assert response.json() == {
         "int_val": 1,
@@ -922,6 +1062,10 @@ def test_nullable_with_non_null_default_pass_value(path: str):
 )
 def test_nullable_with_non_null_default_no_embed_pass_value(path: str, value: Any):
     client = TestClient(app)
-    response = client.post(path, json=value)
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.post(path, json=value)
+
+    assert mock_convert.call_count == 1, "Validator should be called once for the field"
     assert response.status_code == 200, response.text
     assert response.json() == {"val": value}