Revert "Fixed #20462 - Fixed sqlite regex lookups for null values and non-string fields."

This reverts commit 64041f0e6e.

lookup.tests.LookupTests.test_regex_non_string fails under Postgres.
We should also try to rewrite the test using an existing model.

AUTHORS

@@ -270,7 +270,6 @@ answer newbie questions, and generally made Django that much better:
     Brian Harring <ferringb@gmail.com>
     Brant Harris
     Ronny Haryanto <http://ronny.haryan.to/>
-    Axel Haustant <noirbizarre@gmail.com>
     Hawkeye
     Kent Hauser <kent@khauser.net>
     Joe Heck <http://www.rhonabwy.com/wp/>

django/db/backends/sqlite3/base.py

@@ -519,4 +519,4 @@ def _sqlite_format_dtdelta(dt, conn, days, secs, usecs):
     return str(dt)
 
 def _sqlite_regexp(re_pattern, re_string):
-    return bool(re.search(re_pattern, str(re_string))) if re_string is not None else False
+    return bool(re.search(re_pattern, re_string))

tests/lookup/models.py

@@ -57,12 +57,3 @@ class Player(models.Model):
 
     def __str__(self):
         return self.name
-
-
-@python_2_unicode_compatible
-class RegexTestModel(models.Model):
-    name = models.CharField(max_length=100, null=True)
-    integer = models.IntegerField(null=True)
-
-    def __str__(self):
-        return self.name

tests/lookup/tests.py

@@ -6,7 +6,7 @@ from operator import attrgetter
 from django.core.exceptions import FieldError
 from django.test import TestCase, skipUnlessDBFeature
 
-from .models import Author, Article, Tag, Game, Season, Player, RegexTestModel
+from .models import Author, Article, Tag, Game, Season, Player
 
 
 class LookupTests(TestCase):
@@ -610,21 +610,6 @@ class LookupTests(TestCase):
         self.assertQuerysetEqual(Article.objects.filter(headline__regex=r'b(.).*b\1'),
             ['<Article: barfoobaz>', '<Article: bazbaRFOO>', '<Article: foobarbaz>'])
 
-    def test_regex_null(self):
-        """
-        Ensure that a regex lookup does not fail on null/None values
-        """
-        RegexTestModel.objects.create(name=None)
-        self.assertQuerysetEqual(RegexTestModel.objects.filter(name__regex=r'^$'), [])
-
-    def test_regex_non_string(self):
-        """
-        Ensure that a regex lookup does not fail on non-string fields
-        """
-        RegexTestModel.objects.create(name='test', integer=5)
-        self.assertQuerysetEqual(RegexTestModel.objects.filter(integer__regex=r'^5$'),
-            ['<RegexTestModel: test>'])
-
     def test_nonfield_lookups(self):
         """
         Ensure that a lookup query containing non-fields raises the proper