Fixes #100, allow None to get sent to the database regardless of …

…whether the

field in question is nullable.  This prevents the None from getting cast
to a value appropriate to the field and will result in IntegrityErrors.
This is *more* desirable than non-null values getting stored
incorrectly.  Especial thanks to @mkosler for being insistent on this.

peewee.py

@@ -2241,7 +2241,7 @@ def render_field_template(self, quote_char=''):
         return self.field_template % params
 
     def db_value(self, value):
-        if (self.null and value is None):
+        if value is None:
             return None
         return self.column.db_value(value)
 

tests.py

@@ -66,7 +66,7 @@ def __unicode__(self):
 class Entry(TestModel):
     pk = PrimaryKeyField()
     title = CharField(max_length=50, verbose_name='Wacky title')
-    content = TextField()
+    content = TextField(default='')
     pub_date = DateTimeField(null=True)
     blog = ForeignKeyField(Blog, cascade=True)
 
@@ -97,7 +97,7 @@ class EntryTwo(Entry):
 class User(TestModel):
     username = CharField(max_length=50)
     blog = ForeignKeyField(Blog, null=True)
-    active = BooleanField(db_index=True)
+    active = BooleanField(db_index=True, default=False)
 
     class Meta:
         db_table = 'users'
@@ -2138,7 +2138,7 @@ def test_select_related_multiple(self):
         # didn't select title/content/pub_date on entries, so make sure they're none
         for r in results:
             self.assertEqual(r.entry.title, None)
-            self.assertEqual(r.entry.content, None)
+            self.assertEqual(r.entry.content, '') # <-- default value
             self.assertEqual(r.entry.pub_date, None)
             self.assertFalse(r.entry.pk == None)