diff --git a/tests/test_request_params/test_query/test_nullable_and_defaults.py b/tests/test_request_params/test_query/test_nullable_and_defaults.py
new file mode 100644
index 0000000000..bca69444d0
--- /dev/null
+++ b/tests/test_request_params/test_query/test_nullable_and_defaults.py
@@ -0,0 +1,480 @@
+from typing import Annotated, Any, Union
+from unittest.mock import Mock, patch
+
+import pytest
+from dirty_equals import IsList, IsOneOf
+from fastapi import FastAPI, Query
+from fastapi.testclient import TestClient
+from pydantic import BaseModel, BeforeValidator, field_validator
+
+app = FastAPI()
+
+
+def convert(v: Any) -> Any:
+    return v
+
+
+# =====================================================================================
+# Nullable required
+
+
+@app.get("/nullable-required")
+async def read_nullable_required(
+    int_val: Annotated[
+        Union[int, None],
+        BeforeValidator(lambda v: convert(v)),
+    ],
+    str_val: Annotated[
+        Union[str, None],
+        BeforeValidator(lambda v: convert(v)),
+    ],
+    list_val: Annotated[
+        Union[list[int], None],
+        Query(),
+        BeforeValidator(lambda v: convert(v)),
+    ],
+):
+    return {
+        "int_val": int_val,
+        "str_val": str_val,
+        "list_val": list_val,
+        "fields_set": None,
+    }
+
+
+class ModelNullableRequired(BaseModel):
+    int_val: Union[int, None]
+    str_val: Union[str, None]
+    list_val: Union[list[int], None]
+
+    @field_validator("*", mode="before")
+    @classmethod
+    def convert_all(cls, v: Any) -> Any:
+        return convert(v)
+
+
+@app.get("/model-nullable-required")
+async def read_model_nullable_required(
+    params: Annotated[ModelNullableRequired, Query()],
+):
+    return {
+        "int_val": params.int_val,
+        "str_val": params.str_val,
+        "list_val": params.list_val,
+        "fields_set": params.model_fields_set,
+    }
+
+
+@pytest.mark.parametrize(
+    "path",
+    [
+        "/nullable-required",
+        "/model-nullable-required",
+    ],
+)
+def test_nullable_required_schema(path: str):
+    assert app.openapi()["paths"][path]["get"]["parameters"] == [
+        {
+            "required": True,
+            "schema": {
+                "title": "Int Val",
+                "anyOf": [{"type": "integer"}, {"type": "null"}],
+            },
+            "name": "int_val",
+            "in": "query",
+        },
+        {
+            "required": True,
+            "schema": {
+                "title": "Str Val",
+                "anyOf": [{"type": "string"}, {"type": "null"}],
+            },
+            "name": "str_val",
+            "in": "query",
+        },
+        {
+            "in": "query",
+            "name": "list_val",
+            "required": True,
+            "schema": {
+                "anyOf": [
+                    {"items": {"type": "integer"}, "type": "array"},
+                    {"type": "null"},
+                ],
+                "title": "List Val",
+            },
+        },
+    ]
+
+
+@pytest.mark.parametrize(
+    "path",
+    [
+        "/nullable-required",
+        "/model-nullable-required",
+    ],
+)
+def test_nullable_required_missing(path: str):
+    client = TestClient(app)
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.get(path)
+
+    assert mock_convert.call_count == 0, (
+        "Validator should not be called if the value is missing"
+    )
+    assert response.status_code == 422
+    assert response.json() == {
+        "detail": [
+            {
+                "type": "missing",
+                "loc": ["query", "int_val"],
+                "msg": "Field required",
+                "input": IsOneOf(None, {}),
+            },
+            {
+                "type": "missing",
+                "loc": ["query", "str_val"],
+                "msg": "Field required",
+                "input": IsOneOf(None, {}),
+            },
+            {
+                "type": "missing",
+                "loc": ["query", "list_val"],
+                "msg": "Field required",
+                "input": IsOneOf(None, {}),
+            },
+        ]
+    }
+
+
+@pytest.mark.parametrize(
+    "path",
+    [
+        "/nullable-required",
+        "/model-nullable-required",
+    ],
+)
+def test_nullable_required_pass_value(path: str):
+    client = TestClient(app)
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.get(
+            path, params={"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,
+        "str_val": "test",
+        "list_val": [1, 2],
+        "fields_set": IsOneOf(
+            None, IsList("int_val", "str_val", "list_val", check_order=False)
+        ),
+    }
+
+
+# =====================================================================================
+# Nullable with default=None
+
+
+@app.get("/nullable-non-required")
+async def read_nullable_non_required(
+    int_val: Annotated[
+        Union[int, None],
+        BeforeValidator(lambda v: convert(v)),
+    ] = None,
+    str_val: Annotated[
+        Union[str, None],
+        BeforeValidator(lambda v: convert(v)),
+    ] = None,
+    list_val: Annotated[
+        Union[list[int], None],
+        Query(),
+        BeforeValidator(lambda v: convert(v)),
+    ] = None,
+):
+    return {
+        "int_val": int_val,
+        "str_val": str_val,
+        "list_val": list_val,
+        "fields_set": None,
+    }
+
+
+class ModelNullableNonRequired(BaseModel):
+    int_val: Union[int, None] = None
+    str_val: Union[str, None] = None
+    list_val: Union[list[int], None] = None
+
+    @field_validator("*", mode="before")
+    @classmethod
+    def convert_all(cls, v: Any) -> Any:
+        return convert(v)
+
+
+@app.get("/model-nullable-non-required")
+async def read_model_nullable_non_required(
+    params: Annotated[ModelNullableNonRequired, Query()],
+):
+    return {
+        "int_val": params.int_val,
+        "str_val": params.str_val,
+        "list_val": params.list_val,
+        "fields_set": params.model_fields_set,
+    }
+
+
+@pytest.mark.parametrize(
+    "path",
+    [
+        "/nullable-non-required",
+        "/model-nullable-non-required",
+    ],
+)
+def test_nullable_non_required_schema(path: str):
+    assert app.openapi()["paths"][path]["get"]["parameters"] == [
+        {
+            "required": False,
+            "schema": {
+                "title": "Int Val",
+                "anyOf": [{"type": "integer"}, {"type": "null"}],
+                # "default": None, # `None` values are omitted in OpenAPI schema
+            },
+            "name": "int_val",
+            "in": "query",
+        },
+        {
+            "required": False,
+            "schema": {
+                "title": "Str Val",
+                "anyOf": [{"type": "string"}, {"type": "null"}],
+                # "default": None, # `None` values are omitted in OpenAPI schema
+            },
+            "name": "str_val",
+            "in": "query",
+        },
+        {
+            "in": "query",
+            "name": "list_val",
+            "required": False,
+            "schema": {
+                "anyOf": [
+                    {"items": {"type": "integer"}, "type": "array"},
+                    {"type": "null"},
+                ],
+                "title": "List Val",
+                # "default": None, # `None` values are omitted in OpenAPI schema
+            },
+        },
+    ]
+
+
+@pytest.mark.parametrize(
+    "path",
+    [
+        "/nullable-non-required",
+        "/model-nullable-non-required",
+    ],
+)
+def test_nullable_non_required_missing(path: str):
+    client = TestClient(app)
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.get(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() == {
+        "int_val": None,
+        "str_val": None,
+        "list_val": None,
+        "fields_set": IsOneOf(None, []),
+    }
+
+
+@pytest.mark.parametrize(
+    "path",
+    [
+        "/nullable-non-required",
+        "/model-nullable-non-required",
+    ],
+)
+def test_nullable_non_required_pass_value(path: str):
+    client = TestClient(app)
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.get(
+            path, params={"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,
+        "str_val": "test",
+        "list_val": [1, 2],
+        "fields_set": IsOneOf(
+            None, IsList("int_val", "str_val", "list_val", check_order=False)
+        ),
+    }
+
+
+# =====================================================================================
+# Nullable with not-None default
+
+
+@app.get("/nullable-with-non-null-default")
+async def read_nullable_with_non_null_default(
+    *,
+    int_val: Annotated[
+        Union[int, None],
+        BeforeValidator(lambda v: convert(v)),
+    ] = -1,
+    str_val: Annotated[
+        Union[str, None],
+        BeforeValidator(lambda v: convert(v)),
+    ] = "default",
+    list_val: Annotated[
+        Union[list[int], None],
+        Query(default_factory=lambda: [0]),
+        BeforeValidator(lambda v: convert(v)),
+    ],
+):
+    return {
+        "int_val": int_val,
+        "str_val": str_val,
+        "list_val": list_val,
+        "fields_set": None,
+    }
+
+
+class ModelNullableWithNonNullDefault(BaseModel):
+    int_val: Union[int, None] = -1
+    str_val: Union[str, None] = "default"
+    list_val: Union[list[int], None] = [0]
+
+    @field_validator("*", mode="before")
+    @classmethod
+    def convert_all(cls, v: Any) -> Any:
+        return convert(v)
+
+
+@app.get("/model-nullable-with-non-null-default")
+async def read_model_nullable_with_non_null_default(
+    params: Annotated[ModelNullableWithNonNullDefault, Query()],
+):
+    return {
+        "int_val": params.int_val,
+        "str_val": params.str_val,
+        "list_val": params.list_val,
+        "fields_set": params.model_fields_set,
+    }
+
+
+@pytest.mark.parametrize(
+    "path",
+    [
+        pytest.param(
+            "/nullable-with-non-null-default",
+            marks=pytest.mark.xfail(
+                reason="`default_factory` is not reflected in OpenAPI schema"
+            ),
+        ),
+        "/model-nullable-with-non-null-default",
+    ],
+)
+def test_nullable_with_non_null_default_schema(path: str):
+    assert app.openapi()["paths"][path]["get"]["parameters"] == [
+        {
+            "required": False,
+            "schema": {
+                "title": "Int Val",
+                "anyOf": [{"type": "integer"}, {"type": "null"}],
+                "default": -1,
+            },
+            "name": "int_val",
+            "in": "query",
+        },
+        {
+            "required": False,
+            "schema": {
+                "title": "Str Val",
+                "anyOf": [{"type": "string"}, {"type": "null"}],
+                "default": "default",
+            },
+            "name": "str_val",
+            "in": "query",
+        },
+        {
+            "in": "query",
+            "name": "list_val",
+            "required": False,
+            "schema": {
+                "anyOf": [
+                    {"items": {"type": "integer"}, "type": "array"},
+                    {"type": "null"},
+                ],
+                "title": "List Val",
+                "default": [0],  # `default_factory` is not reflected in OpenAPI schema
+            },
+        },
+    ]
+
+
+@pytest.mark.parametrize(
+    "path",
+    [
+        "/nullable-with-non-null-default",
+        "/model-nullable-with-non-null-default",
+    ],
+)
+@pytest.mark.xfail(
+    reason="Missing parameters are pre-populated with default values before validation"
+)
+def test_nullable_with_non_null_default_missing(path: str):
+    client = TestClient(app)
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.get(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() == {
+        "int_val": -1,
+        "str_val": "default",
+        "list_val": [0],
+        "fields_set": IsOneOf(None, []),
+    }
+
+
+@pytest.mark.parametrize(
+    "path",
+    [
+        "/nullable-with-non-null-default",
+        "/model-nullable-with-non-null-default",
+    ],
+)
+def test_nullable_with_non_null_default_pass_value(path: str):
+    client = TestClient(app)
+
+    with patch(f"{__name__}.convert", Mock(wraps=convert)) as mock_convert:
+        response = client.get(
+            path, params={"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,
+        "str_val": "test",
+        "list_val": [1, 2],
+        "fields_set": IsOneOf(
+            None, IsList("int_val", "str_val", "list_val", check_order=False)
+        ),
+    }