diff --git a/graphene/tests/issues/test_881.py b/graphene/tests/issues/test_881.py
new file mode 100644
index 00000000..f97b5917
--- /dev/null
+++ b/graphene/tests/issues/test_881.py
@@ -0,0 +1,27 @@
+import pickle
+
+from ...types.enum import Enum
+
+
+class PickleEnum(Enum):
+    # is defined outside of test because pickle unable to dump class inside ot pytest function
+    A = "a"
+    B = 1
+
+
+def test_enums_pickling():
+    a = PickleEnum.A
+    pickled = pickle.dumps(a)
+    restored = pickle.loads(pickled)
+    assert type(a) is type(restored)
+    assert a == restored
+    assert a.value == restored.value
+    assert a.name == restored.name
+
+    b = PickleEnum.B
+    pickled = pickle.dumps(b)
+    restored = pickle.loads(pickled)
+    assert type(a) is type(restored)
+    assert b == restored
+    assert b.value == restored.value
+    assert b.name == restored.name
diff --git a/graphene/types/enum.py b/graphene/types/enum.py
index 58e65c69..d3469a15 100644
--- a/graphene/types/enum.py
+++ b/graphene/types/enum.py
@@ -31,9 +31,11 @@ class EnumMeta(SubclassWithMeta_Meta):
         # with the enum values.
         enum_members.pop("Meta", None)
         enum = PyEnum(cls.__name__, enum_members)
-        return SubclassWithMeta_Meta.__new__(
+        obj = SubclassWithMeta_Meta.__new__(
             cls, name_, bases, dict(classdict, __enum__=enum), **options
         )
+        globals()[name_] = obj.__enum__
+        return obj
 
     def get(cls, value):
         return cls._meta.enum(value)
@@ -63,7 +65,7 @@ class EnumMeta(SubclassWithMeta_Meta):
         cls, enum, name=None, description=None, deprecation_reason=None
     ):  # noqa: N805
         name = name or enum.__name__
-        description = description or enum.__doc__
+        description = description or enum.__doc__ or "An enumeration."
         meta_dict = {
             "enum": enum,
             "description": description,
diff --git a/graphene/types/inputobjecttype.py b/graphene/types/inputobjecttype.py
index c0454aba..257f48be 100644
--- a/graphene/types/inputobjecttype.py
+++ b/graphene/types/inputobjecttype.py
@@ -15,6 +15,31 @@ class InputObjectTypeOptions(BaseOptions):
     container = None  # type: InputObjectTypeContainer
 
 
+# Currently in Graphene, we get a `None` whenever we access an (optional) field that was not set in an InputObjectType
+# using the InputObjectType.<attribute> dot access syntax. This is ambiguous, because in this current (Graphene
+# historical) arrangement, we cannot distinguish between a field not being set and a field being set to None.
+# At the same time, we shouldn't break existing code that expects a `None` when accessing a field that was not set.
+_INPUT_OBJECT_TYPE_DEFAULT_VALUE = None
+
+# To mitigate this, we provide the function `set_input_object_type_default_value` to allow users to change the default
+# value returned in non-specified fields in InputObjectType to another meaningful sentinel value (e.g. Undefined)
+# if they want to. This way, we can keep code that expects a `None` working while we figure out a better solution (or
+# a well-documented breaking change) for this issue.
+
+
+def set_input_object_type_default_value(default_value):
+    """
+    Change the sentinel value returned by non-specified fields in an InputObjectType
+    Useful to differentiate between a field not being set and a field being set to None by using a sentinel value
+    (e.g. Undefined is a good sentinel value for this purpose)
+
+    This function should be called at the beginning of the app or in some other place where it is guaranteed to
+    be called before any InputObjectType is defined.
+    """
+    global _INPUT_OBJECT_TYPE_DEFAULT_VALUE
+    _INPUT_OBJECT_TYPE_DEFAULT_VALUE = default_value
+
+
 class InputObjectTypeContainer(dict, BaseType):  # type: ignore
     class Meta:
         abstract = True
@@ -22,7 +47,7 @@ class InputObjectTypeContainer(dict, BaseType):  # type: ignore
     def __init__(self, *args, **kwargs):
         dict.__init__(self, *args, **kwargs)
         for key in self._meta.fields:
-            setattr(self, key, self.get(key, None))
+            setattr(self, key, self.get(key, _INPUT_OBJECT_TYPE_DEFAULT_VALUE))
 
     def __init_subclass__(cls, *args, **kwargs):
         pass
diff --git a/graphene/types/tests/conftest.py b/graphene/types/tests/conftest.py
new file mode 100644
index 00000000..43f7d726
--- /dev/null
+++ b/graphene/types/tests/conftest.py
@@ -0,0 +1,12 @@
+import pytest
+from graphql import Undefined
+
+from graphene.types.inputobjecttype import set_input_object_type_default_value
+
+
+@pytest.fixture()
+def set_default_input_object_type_to_undefined():
+    """This fixture is used to change the default value of optional inputs in InputObjectTypes for specific tests"""
+    set_input_object_type_default_value(Undefined)
+    yield
+    set_input_object_type_default_value(None)
diff --git a/graphene/types/tests/test_enum.py b/graphene/types/tests/test_enum.py
index 9b3082df..e6fce66c 100644
--- a/graphene/types/tests/test_enum.py
+++ b/graphene/types/tests/test_enum.py
@@ -65,6 +65,21 @@ def test_enum_from_builtin_enum():
     assert RGB.BLUE
 
 
+def test_enum_custom_description_in_constructor():
+    description = "An enumeration, but with a custom description"
+    RGB = Enum(
+        "RGB",
+        "RED,GREEN,BLUE",
+        description=description,
+    )
+    assert RGB._meta.description == description
+
+
+def test_enum_from_python3_enum_uses_default_builtin_doc():
+    RGB = Enum("RGB", "RED,GREEN,BLUE")
+    assert RGB._meta.description == "An enumeration."
+
+
 def test_enum_from_builtin_enum_accepts_lambda_description():
     def custom_description(value):
         if not value:
diff --git a/graphene/types/tests/test_inputobjecttype.py b/graphene/types/tests/test_inputobjecttype.py
index 0fb7e394..0d7bcf80 100644
--- a/graphene/types/tests/test_inputobjecttype.py
+++ b/graphene/types/tests/test_inputobjecttype.py
@@ -1,3 +1,5 @@
+from graphql import Undefined
+
 from ..argument import Argument
 from ..field import Field
 from ..inputfield import InputField
@@ -6,6 +8,7 @@ from ..objecttype import ObjectType
 from ..scalars import Boolean, String
 from ..schema import Schema
 from ..unmountedtype import UnmountedType
+from ... import NonNull
 
 
 class MyType:
@@ -136,3 +139,31 @@ def test_inputobjecttype_of_input():
 
     assert not result.errors
     assert result.data == {"isChild": True}
+
+
+def test_inputobjecttype_default_input_as_undefined(
+    set_default_input_object_type_to_undefined,
+):
+    class TestUndefinedInput(InputObjectType):
+        required_field = String(required=True)
+        optional_field = String()
+
+    class Query(ObjectType):
+        undefined_optionals_work = Field(NonNull(Boolean), input=TestUndefinedInput())
+
+        def resolve_undefined_optionals_work(self, info, input: TestUndefinedInput):
+            # Confirm that optional_field comes as Undefined
+            return (
+                input.required_field == "required" and input.optional_field is Undefined
+            )
+
+    schema = Schema(query=Query)
+    result = schema.execute(
+        """query basequery {
+        undefinedOptionalsWork(input: {requiredField: "required"})
+    }
+    """
+    )
+
+    assert not result.errors
+    assert result.data == {"undefinedOptionalsWork": True}
diff --git a/graphene/types/tests/test_type_map.py b/graphene/types/tests/test_type_map.py
index 55b1706e..55665b6b 100644
--- a/graphene/types/tests/test_type_map.py
+++ b/graphene/types/tests/test_type_map.py
@@ -20,8 +20,8 @@ from ..inputobjecttype import InputObjectType
 from ..interface import Interface
 from ..objecttype import ObjectType
 from ..scalars import Int, String
-from ..structures import List, NonNull
 from ..schema import Schema
+from ..structures import List, NonNull
 
 
 def create_type_map(types, auto_camelcase=True):
@@ -227,6 +227,18 @@ def test_inputobject():
     assert foo_field.description == "Field description"
 
 
+def test_inputobject_undefined(set_default_input_object_type_to_undefined):
+    class OtherObjectType(InputObjectType):
+        optional_field = String()
+
+    type_map = create_type_map([OtherObjectType])
+    assert "OtherObjectType" in type_map
+    graphql_type = type_map["OtherObjectType"]
+
+    container = graphql_type.out_type({})
+    assert container.optional_field is Undefined
+
+
 def test_objecttype_camelcase():
     class MyObjectType(ObjectType):
         """Description"""
diff --git a/graphene/validation/depth_limit.py b/graphene/validation/depth_limit.py
index b4599e66..e0f28663 100644
--- a/graphene/validation/depth_limit.py
+++ b/graphene/validation/depth_limit.py
@@ -30,7 +30,7 @@ try:
 except ImportError:
     # backwards compatibility for v3.6
     from typing import Pattern
-from typing import Callable, Dict, List, Optional, Union
+from typing import Callable, Dict, List, Optional, Union, Tuple
 
 from graphql import GraphQLError
 from graphql.validation import ValidationContext, ValidationRule
@@ -82,7 +82,7 @@ def depth_limit_validator(
 
 
 def get_fragments(
-    definitions: List[DefinitionNode],
+    definitions: Tuple[DefinitionNode, ...],
 ) -> Dict[str, FragmentDefinitionNode]:
     fragments = {}
     for definition in definitions:
@@ -94,7 +94,7 @@ def get_fragments(
 # This will actually get both queries and mutations.
 # We can basically treat those the same
 def get_queries_and_mutations(
-    definitions: List[DefinitionNode],
+    definitions: Tuple[DefinitionNode, ...],
 ) -> Dict[str, OperationDefinitionNode]:
     operations = {}