Fixed some bugs regarding has_one relations.

generate.py

@@ -130,7 +130,11 @@ class Model(object):
     def add_foreign_key(self, name, models):
         self.foreign_keys.append(name)
         singular = re.sub('_' + PRIMARY_KEY + '$', '', name)
-        other_model = find_model(singular, models)
+
+        try:
+            other_model = find_model(singular, models)
+        except ValueError:
+            return
 
         self.belongs_to.append((singular, self.relopts(other_model)))
         other_model.add_has_relation(self)
@@ -278,7 +282,7 @@ if __name__ == '__main__':
     parser.add_argument('--has-one', nargs=2, dest='opt_has_one',
                         help='one-to-one relationships of the form '
                         '\'payment-receipt\', where one payment has one '
-                        'receipt', action='append')
+                        'receipt', action='append', default=[])
     parser.add_argument('--namespace', default='', dest='opt_namespace',
                         help='PHP namespace to create models classes in')
     parser.add_argument('--create-select', action='store_true',