Add support for empty var with None default value

CHANGELOG.rst

@@ -16,6 +16,8 @@ Added
 - Added option to override existing variables with ``read_env``
   `#103 <https://github.com/joke2k/django-environ/issues/103>`_,
   `#249 <https://github.com/joke2k/django-environ/issues/249>`_.
+- Added support for empty var with None default value
+  `#209 <https://github.com/joke2k/django-environ/issues/209>`_.
 
 
 Fixed

environ/environ.py

@@ -375,6 +375,8 @@ def get_value(self, var, cast=None, default=NOTSET, parse_default=False):
                     not isinstance(default, NoValue):
                 cast = type(default)
 
+        value = None if default is None and value == '' else value
+
         if value != default or (parse_default and value):
             value = self.parse_value(value, cast)
 

tests/test_env.py

@@ -86,6 +86,7 @@ def test_int(self):
 
     def test_int_with_none_default(self):
         assert self.env('NOT_PRESENT_VAR', cast=int, default=None) is None
+        assert self.env('EMPTY_INT_VAR', cast=int, default=None) is None
 
     @pytest.mark.parametrize(
         'value,variable',

tests/test_env.txt

@@ -29,6 +29,7 @@ FLOAT_STRANGE_VAR2=123.420.333,3
 FLOAT_NEGATIVE_VAR=-1.0
 PROXIED_VAR=$STR_VAR
 EMPTY_LIST=
+EMPTY_INT_VAR=
 INT_VAR=42
 STR_LIST_WITH_SPACES= foo,  bar
 STR_VAR=bar