diff --git a/django/test/client.py b/django/test/client.py
index d14ba43792..07641b7e65 100644
--- a/django/test/client.py
+++ b/django/test/client.py
@@ -192,7 +192,12 @@ def encode_multipart(boundary, data):
     # file, or a *list* of form values and/or files. Remember that HTTP field
     # names can be duplicated!
     for (key, value) in data.items():
-        if is_file(value):
+        if value is None:
+            raise TypeError(
+                'Cannot encode None as POST data. Did you mean to pass an '
+                'empty string or omit the value?'
+            )
+        elif is_file(value):
             lines.extend(encode_file(boundary, key, value))
         elif not isinstance(value, str) and is_iterable(value):
             for item in value:
diff --git a/django/utils/http.py b/django/utils/http.py
index db18e57803..de1ea71368 100644
--- a/django/utils/http.py
+++ b/django/utils/http.py
@@ -91,20 +91,31 @@ def urlencode(query, doseq=False):
         query = query.items()
     query_params = []
     for key, value in query:
-        if isinstance(value, (str, bytes)):
+        if value is None:
+            raise TypeError(
+                'Cannot encode None in a query string. Did you mean to pass '
+                'an empty string or omit the value?'
+            )
+        elif isinstance(value, (str, bytes)):
             query_val = value
         else:
             try:
-                iter(value)
+                itr = iter(value)
             except TypeError:
                 query_val = value
             else:
                 # Consume generators and iterators, even when doseq=True, to
                 # work around https://bugs.python.org/issue31706.
-                query_val = [
-                    item if isinstance(item, bytes) else str(item)
-                    for item in value
-                ]
+                query_val = []
+                for item in itr:
+                    if item is None:
+                        raise TypeError(
+                            'Cannot encode None in a query string. Did you '
+                            'mean to pass an empty string or omit the value?'
+                        )
+                    elif not isinstance(item, bytes):
+                        item = str(item)
+                    query_val.append(item)
         query_params.append((key, query_val))
     return original_urlencode(query_params, doseq)
 
diff --git a/docs/releases/2.2.txt b/docs/releases/2.2.txt
index f731562640..3201d00047 100644
--- a/docs/releases/2.2.txt
+++ b/docs/releases/2.2.txt
@@ -457,6 +457,11 @@ Miscellaneous
 * Tests that violate deferrable database constraints now error when run on
   SQLite 3.20+, just like on other backends that support such constraints.
 
+* To catch usage mistakes, the test :class:`~django.test.Client` and
+  :func:`django.utils.http.urlencode` now raise ``TypeError`` if ``None`` is
+  passed as a value to encode because ``None`` can't be encoded in GET and POST
+  data. Either pass an empty string or omit the value.
+
 .. _deprecated-features-2.2:
 
 Features deprecated in 2.2
diff --git a/tests/test_client/tests.py b/tests/test_client/tests.py
index bb6c8bbff0..432865328f 100644
--- a/tests/test_client/tests.py
+++ b/tests/test_client/tests.py
@@ -59,6 +59,14 @@ class ClientTest(TestCase):
         response = self.client.get('/get_view/?var=1\ufffd')
         self.assertEqual(response.context['var'], '1\ufffd')
 
+    def test_get_data_none(self):
+        msg = (
+            'Cannot encode None in a query string. Did you mean to pass an '
+            'empty string or omit the value?'
+        )
+        with self.assertRaisesMessage(TypeError, msg):
+            self.client.get('/get_view/', {'value': None})
+
     def test_get_post_view(self):
         "GET a view that normally expects POSTs"
         response = self.client.get('/post_view/', {})
@@ -92,6 +100,14 @@ class ClientTest(TestCase):
         self.assertEqual(response.templates[0].name, 'POST Template')
         self.assertContains(response, 'Data received')
 
+    def test_post_data_none(self):
+        msg = (
+            'Cannot encode None as POST data. Did you mean to pass an empty '
+            'string or omit the value?'
+        )
+        with self.assertRaisesMessage(TypeError, msg):
+            self.client.post('/post_view/', {'value': None})
+
     def test_json_serialization(self):
         """The test client serializes JSON data."""
         methods = ('post', 'put', 'patch', 'delete')
diff --git a/tests/utils_tests/test_http.py b/tests/utils_tests/test_http.py
index 93f45fb936..aca825ef1f 100644
--- a/tests/utils_tests/test_http.py
+++ b/tests/utils_tests/test_http.py
@@ -12,7 +12,12 @@ from django.utils.http import (
 )
 
 
-class URLEncodeTests(unittest.TestCase):
+class URLEncodeTests(SimpleTestCase):
+    cannot_encode_none_msg = (
+        'Cannot encode None in a query string. Did you mean to pass an '
+        'empty string or omit the value?'
+    )
+
     def test_tuples(self):
         self.assertEqual(urlencode((('a', 1), ('b', 2), ('c', 3))), 'a=1&b=2&c=3')
 
@@ -65,6 +70,20 @@ class URLEncodeTests(unittest.TestCase):
         self.assertEqual(urlencode({'a': gen()}, doseq=True), 'a=0&a=1')
         self.assertEqual(urlencode({'a': gen()}, doseq=False), 'a=%5B%270%27%2C+%271%27%5D')
 
+    def test_none(self):
+        with self.assertRaisesMessage(TypeError, self.cannot_encode_none_msg):
+            urlencode({'a': None})
+
+    def test_none_in_sequence(self):
+        with self.assertRaisesMessage(TypeError, self.cannot_encode_none_msg):
+            urlencode({'a': [None]}, doseq=True)
+
+    def test_none_in_generator(self):
+        def gen():
+            yield None
+        with self.assertRaisesMessage(TypeError, self.cannot_encode_none_msg):
+            urlencode({'a': gen()}, doseq=True)
+
 
 class Base36IntTests(SimpleTestCase):
     def test_roundtrip(self):