diff --git a/openapi_python_client/parser/properties.py b/openapi_python_client/parser/properties.py
index 88db0b7a9..c1076e9dd 100644
--- a/openapi_python_client/parser/properties.py
+++ b/openapi_python_client/parser/properties.py
@@ -64,7 +64,9 @@ def get_imports(self, *, prefix: str) -> Set[str]:
             back to the root of the generated client.
         """
         if self.nullable or not self.required:
-            return {"from typing import Optional"}
+            return {"from typing import Optional",
+                    "from typing import cast",
+                    f"from {prefix}types import UNSET"}
         return set()
 
     def to_string(self) -> str:
@@ -72,15 +74,28 @@ def to_string(self) -> str:
         if self.default:
             default = self.default
         elif not self.required:
-            default = "None"
+            default = "cast(None, UNSET)"
         else:
             default = None
 
         if default is not None:
-            return f"{self.python_name}: {self.get_type_string()} = {self.default}"
+            return f"{self.python_name}: {self.get_type_string()} = {default}"
         else:
             return f"{self.python_name}: {self.get_type_string()}"
 
+    def to_query_method_arg(self) -> str:
+        """ How this should be declared in a query string """
+        if self.default:
+            default = self.default
+        elif not self.required:
+            default = "None"
+        else:
+            default = None
+
+        if default is not None:
+            return f"{self.python_name}: {self.get_type_string()} = {default}"
+        else:
+            return f"{self.python_name}: {self.get_type_string()}"
 
 @dataclass
 class StringProperty(Property):
diff --git a/openapi_python_client/templates/endpoint_macros.pyi b/openapi_python_client/templates/endpoint_macros.pyi
index 7fe2ca053..1d5df8c23 100644
--- a/openapi_python_client/templates/endpoint_macros.pyi
+++ b/openapi_python_client/templates/endpoint_macros.pyi
@@ -80,7 +80,7 @@ client: Client,
 {% endif %}
 {# path parameters #}
 {% for parameter in endpoint.path_parameters %}
-{{ parameter.to_string() }},
+{{parameter.to_query_method_arg()}},
 {% endfor %}
 {# Form data if any #}
 {% if endpoint.form_body_reference %}
@@ -96,10 +96,10 @@ json_body: {{ endpoint.json_body.get_type_string() }},
 {% endif %}
 {# query parameters #}
 {% for parameter in endpoint.query_parameters %}
-{{ parameter.to_string() }},
+{{parameter.to_query_method_arg()}},
 {% endfor %}
 {% for parameter in endpoint.header_parameters %}
-{{ parameter.to_string() }},
+{{ parameter.to_query_method_arg() }},
 {% endfor %}
 {% endmacro %}
 
diff --git a/openapi_python_client/templates/model.pyi b/openapi_python_client/templates/model.pyi
index 899256b2d..4aa246273 100644
--- a/openapi_python_client/templates/model.pyi
+++ b/openapi_python_client/templates/model.pyi
@@ -24,11 +24,17 @@ class {{ model.reference.class_name }}:
         {% endif %}
         {% endfor %}
 
-        return {
-            {% for property in model.required_properties + model.optional_properties %}
-            "{{ property.name }}": {{ property.python_name }},
-            {% endfor %}
-        }
+        properties: Dict[str, Any] = dict()
+
+        {% for property in model.required_properties + model.optional_properties %}
+        {% if not property.required %}
+        if {{property.python_name}} is not UNSET:
+            properties["{{ property.name }}"] = {{ property.python_name }}
+        {% else %}
+        properties["{{ property.name }}"] = {{ property.python_name }}
+        {% endif %}
+        {% endfor %}
+        return properties
 
     @staticmethod
     def from_dict(d: Dict[str, Any]) -> "{{ model.reference.class_name }}":
diff --git a/openapi_python_client/templates/property_templates/date_property.pyi b/openapi_python_client/templates/property_templates/date_property.pyi
index 416acc1e1..2ab3b0f10 100644
--- a/openapi_python_client/templates/property_templates/date_property.pyi
+++ b/openapi_python_client/templates/property_templates/date_property.pyi
@@ -12,6 +12,9 @@ if {{ source }} is not None:
 {% if property.required %}
 {{ destination }} = {{ source }}.isoformat()
 {% else %}
-{{ destination }} = {{ source }}.isoformat() if {{ source }} else None
+if {{ source }} is UNSET:
+    {{ destination }} = UNSET
+else:
+    {{ destination }} = {{ source }}.isoformat() if {{ source }} else None
 {% endif %}
 {% endmacro %}
diff --git a/openapi_python_client/templates/property_templates/datetime_property.pyi b/openapi_python_client/templates/property_templates/datetime_property.pyi
index ff57249a5..e3cf3242d 100644
--- a/openapi_python_client/templates/property_templates/datetime_property.pyi
+++ b/openapi_python_client/templates/property_templates/datetime_property.pyi
@@ -12,6 +12,9 @@ if {{ source }} is not None:
 {% if property.required %}
 {{ destination }} = {{ source }}.isoformat()
 {% else %}
-{{ destination }} = {{ source }}.isoformat() if {{ source }} else None
+if {{ source }} is UNSET:
+    {{ destination }} = UNSET
+else:
+    {{ destination }} = {{ source }}.isoformat() if {{ source }} else None
 {% endif %}
 {% endmacro %}
diff --git a/openapi_python_client/templates/property_templates/dict_property.pyi b/openapi_python_client/templates/property_templates/dict_property.pyi
index 2feabd1d2..e4c8a9edc 100644
--- a/openapi_python_client/templates/property_templates/dict_property.pyi
+++ b/openapi_python_client/templates/property_templates/dict_property.pyi
@@ -12,6 +12,9 @@ if {{ source }} is not None:
 {% if property.required %}
 {{ destination }} = {{ source }}
 {% else %}
-{{ destination }} = {{ source }} if {{ source }} else None
+if {{ source }} is UNSET:
+    {{ destination }} = UNSET
+else:
+    {{ destination }} = {{ source }} if {{ source }} else None
 {% endif %}
 {% endmacro %}
diff --git a/openapi_python_client/templates/property_templates/enum_property.pyi b/openapi_python_client/templates/property_templates/enum_property.pyi
index 2cff340c3..e513ab347 100644
--- a/openapi_python_client/templates/property_templates/enum_property.pyi
+++ b/openapi_python_client/templates/property_templates/enum_property.pyi
@@ -1,3 +1,5 @@
+from openapi_python_client.templates.types import UNSET
+
 {% macro construct(property, source) %}
 {% if property.required %}
 {{ property.python_name }} = {{ property.reference.class_name }}({{ source }})
@@ -12,6 +14,9 @@ if {{ source }} is not None:
 {% if property.required %}
 {{ destination }} = {{ source }}.value
 {% else %}
-{{ destination }} = {{ source }}.value if {{ source }} else None
+if {{ source }} is UNSET:
+    {{ destination }} = UNSET
+else:
+    {{ destination }} = {{ source }}.value if {{ source }} else None
 {% endif %}
 {% endmacro %}
diff --git a/openapi_python_client/templates/property_templates/file_property.pyi b/openapi_python_client/templates/property_templates/file_property.pyi
index 444c9dbcb..10914730b 100644
--- a/openapi_python_client/templates/property_templates/file_property.pyi
+++ b/openapi_python_client/templates/property_templates/file_property.pyi
@@ -7,6 +7,9 @@
 {% if property.required %}
 {{ destination }} = {{ source }}.to_tuple()
 {% else %}
-{{ destination }} = {{ source }}.to_tuple() if {{ source }} else None
+if {{ source }} is UNSET:
+    {{ destination }} = UNSET
+else:
+    {{ destination }} = {{ source }}.to_tuple() if {{ source }} else None
 {% endif %}
 {% endmacro %}
diff --git a/openapi_python_client/templates/property_templates/list_property.pyi b/openapi_python_client/templates/property_templates/list_property.pyi
index 015eb0880..2f96d5d87 100644
--- a/openapi_python_client/templates/property_templates/list_property.pyi
+++ b/openapi_python_client/templates/property_templates/list_property.pyi
@@ -1,3 +1,5 @@
+from openapi_python_client.templates.types import UNSET
+
 {% macro construct(property, source) %}
 {% set inner_property = property.inner_property %}
 {% if inner_property.template %}
@@ -36,6 +38,8 @@ for {{ inner_source }} in {{ source }}:
 {% if not property.required %}
 if {{ source }} is None:
     {{ destination }} = None
+elif {{ source }} is UNSET:
+    {{ destination }} = UNSET
 else:
     {{ _transform(property, source, destination) | indent(4) }}
 {% else %}
diff --git a/openapi_python_client/templates/property_templates/ref_property.pyi b/openapi_python_client/templates/property_templates/ref_property.pyi
index c38a5199c..ebd3cd674 100644
--- a/openapi_python_client/templates/property_templates/ref_property.pyi
+++ b/openapi_python_client/templates/property_templates/ref_property.pyi
@@ -12,6 +12,9 @@ if {{ source }} is not None:
 {% if property.required %}
 {{ destination }} = {{ source }}.to_dict()
 {% else %}
-{{ destination }} = {{ source }}.to_dict() if {{ source }} else None
+if {{ source }} is UNSET:
+    {{ destination }} = UNSET
+else:
+    {{ destination }} = {{ source }}.to_dict() if {{ source }} else None
 {% endif %}
 {% endmacro %}
diff --git a/openapi_python_client/templates/property_templates/union_property.pyi b/openapi_python_client/templates/property_templates/union_property.pyi
index 1498d68c7..b4b0e24d9 100644
--- a/openapi_python_client/templates/property_templates/union_property.pyi
+++ b/openapi_python_client/templates/property_templates/union_property.pyi
@@ -25,6 +25,8 @@ def _parse_{{ property.python_name }}(data: Dict[str, Any]) -> {{ property.get_t
 {% if not property.required %}
 if {{ source }} is None:
     {{ destination }}: {{ property.get_type_string() }} = None
+elif {{ source }} is UNSET:
+    {{ destination }} = UNSET
 {% endif %}
 {% for inner_property in property.inner_properties %}
     {% if loop.first and property.required %}{# No if None statement before this #}
@@ -36,7 +38,7 @@ else:
     {% endif %}
 {% if inner_property.template %}
 {% from "property_templates/" + inner_property.template import transform %}
-    {{ transform(inner_property, source, destination) | indent(8) }}
+    {{ transform(inner_property, source, destination) | indent(4) }}
 {% else %}
     {{ destination }} = {{ source }}
 {% endif %}
diff --git a/openapi_python_client/templates/types.py b/openapi_python_client/templates/types.py
index 951227435..84146cef2 100644
--- a/openapi_python_client/templates/types.py
+++ b/openapi_python_client/templates/types.py
@@ -1,8 +1,11 @@
 """ Contains some shared types for properties """
-from typing import BinaryIO, Generic, MutableMapping, Optional, TextIO, Tuple, TypeVar, Union
+from typing import BinaryIO, Generic, MutableMapping, NewType, Optional, TextIO, Tuple, TypeVar, Union
 
 import attr
 
+Unset = NewType("Unset", object)
+UNSET: Unset = Unset(object())
+
 
 @attr.s(auto_attribs=True)
 class File:
diff --git a/tests/test_openapi_parser/test_properties.py b/tests/test_openapi_parser/test_properties.py
index c0f4cea6a..70c25cfbd 100644
--- a/tests/test_openapi_parser/test_properties.py
+++ b/tests/test_openapi_parser/test_properties.py
@@ -43,7 +43,7 @@ def test_to_string(self, mocker):
 
         assert p.to_string() == f"{snake_case(name)}: {get_type_string()}"
         p.required = False
-        assert p.to_string() == f"{snake_case(name)}: {get_type_string()} = None"
+        assert p.to_string() == f"{snake_case(name)}: {get_type_string()} = cast(None, UNSET)"
 
         p.default = "TEST"
         assert p.to_string() == f"{snake_case(name)}: {get_type_string()} = TEST"
@@ -57,7 +57,26 @@ def test_get_imports(self, mocker):
         assert p.get_imports(prefix="") == set()
 
         p.required = False
-        assert p.get_imports(prefix="") == {"from typing import Optional"}
+        assert p.get_imports(prefix="") == {
+            "from types import UNSET",
+            "from typing import Optional",
+            "from typing import cast",
+        }
+
+    def test_to_query_method_arg(self, mocker):
+        from openapi_python_client.parser.properties import Property
+
+        name = mocker.MagicMock()
+        snake_case = mocker.patch("openapi_python_client.utils.snake_case")
+        p = Property(name=name, required=True, default=None, nullable=False)
+        get_type_string = mocker.patch.object(p, "get_type_string")
+
+        assert p.to_query_method_arg() == f"{snake_case(name)}: {get_type_string()}"
+        p.required = False
+        assert p.to_query_method_arg() == f"{snake_case(name)}: {get_type_string()} = None"
+
+        p.default = "TEST"
+        assert p.to_query_method_arg() == f"{snake_case(name)}: {get_type_string()} = TEST"
 
     def test__validate_default(self):
         from openapi_python_client.parser.properties import Property