CharField - add allow_null argument

docs/api-guide/fields.md

@@ -157,23 +157,24 @@ Corresponds to `django.db.models.fields.BooleanField`.
 ## CharField
 
 A text representation, optionally validates the text to be shorter than `max_length` and longer than `min_length`.
+If `allow_none` is `False` (default), `None` values will be converted to an empty string.
 
 Corresponds to `django.db.models.fields.CharField`
 or `django.db.models.fields.TextField`.
 
-**Signature:** `CharField(max_length=None, min_length=None)`
+**Signature:** `CharField(max_length=None, min_length=None, allow_none=False)`
 
 ## URLField
 
 Corresponds to `django.db.models.fields.URLField`.  Uses Django's `django.core.validators.URLValidator` for validation.
 
-**Signature:** `CharField(max_length=200, min_length=None)`
+**Signature:** `CharField(max_length=200, min_length=None, allow_none=False)`
 
 ## SlugField
 
 Corresponds to `django.db.models.fields.SlugField`.
 
-**Signature:** `CharField(max_length=50, min_length=None)`
+**Signature:** `CharField(max_length=50, min_length=None, allow_none=False)`
 
 ## ChoiceField
 

rest_framework/fields.py

@@ -443,8 +443,9 @@ class CharField(WritableField):
     type_label = 'string'
     form_field_class = forms.CharField
 
-    def __init__(self, max_length=None, min_length=None, *args, **kwargs):
+    def __init__(self, max_length=None, min_length=None, allow_none=False, *args, **kwargs):
         self.max_length, self.min_length = max_length, min_length
+        self.allow_none = allow_none
         super(CharField, self).__init__(*args, **kwargs)
         if min_length is not None:
             self.validators.append(validators.MinLengthValidator(min_length))
@@ -452,7 +453,7 @@ class CharField(WritableField):
             self.validators.append(validators.MaxLengthValidator(max_length))
 
     def from_native(self, value):
-        if value is None:
+        if value is None and not self.allow_none:
             return ''
         if isinstance(value, six.string_types):
             return value