Fixed #21856: Don't crash runserver when DATABASES = {}

from django.db.migrations.executor import MigrationExecutor

from django.utils import autoreload

from django.utils import six

from django.core.exceptions import ImproperlyConfigured

naiveip_re = re.compile(r"""^(?:

(?P<addr>

        self.stdout.write("Performing system checks...\n\n")

        self.validate(display_num_errors=True)

        try:

            self.check_migrations()

        except ImproperlyConfigured:

            pass

        now = datetime.now().strftime('%B %d, %Y - %X')

        if six.PY2:

            now = now.decode('utf-8')