Fixed #22411: Throw a more helpful error if contenttypes doesn't exist.

from django.apps import apps

from django.db import models

from django.db.utils import OperationalError, ProgrammingError

from django.utils.translation import ugettext_lazy as _

from django.utils.encoding import smart_text, force_text

from django.utils.encoding import python_2_unicode_compatible

            # We start with get() and not get_or_create() in order to use

            # the db_for_read (see #20401).

            ct = self.get(app_label=opts.app_label, model=opts.model_name)

        except (OperationalError, ProgrammingError):

            # It's possible to migrate a single app before contenttypes,

            # as it's not a required initial dependency (it's contrib!)

            # Have a nice error for this.

            raise RuntimeError("Error creating new content types. Please make sure contenttypes is migrated before trying to migrate apps individually.")

        except self.model.DoesNotExist:

            # Not found in the database; we proceed to create it.  This time we

            # use get_or_create to take care of any race conditions.