misc: defer null-character check in api to submodule initialization (#48114)

src/authentic2/__init__.py

@@ -21,7 +21,6 @@ default_app_config = 'authentic2.app.Authentic2Config'
 if django.VERSION < (2,):
     from . import validators
     from django.forms import fields
-    import rest_framework.fields
 
     # query-string and form parameters used to query database charfield must be checked for NULL characters
     # https://code.djangoproject.com/ticket/30064
@@ -34,4 +33,3 @@ if django.VERSION < (2,):
 
         fields.CharField.__init__ = CharField_new_init__
         fields.CharField.a2_workaround = True
-    rest_framework.fields.ProhibitNullCharactersValidator = validators.ProhibitNullCharactersValidator

src/authentic2/api_views.py

@@ -66,7 +66,11 @@ from .models import Attribute, PasswordReset, Service
 from .a2_rbac.utils import get_default_ou
 
 
-# Retro-compatibility with Django 1.8
+# Retro-compatibility with older Django versions
+if django.VERSION < (2,):
+    import rest_framework.fields
+    from . import validators
+    rest_framework.fields.ProhibitNullCharactersValidator = validators.ProhibitNullCharactersValidator
 if django.VERSION < (1, 11):
     authentication.authenticate = utils.authenticate