Changed all status to start with Uppercase letters, made 3 properties required. Changed all the status to start with Uppercase letters because they are publicly visible. Also changed required=True to False for created_by, modified_by property to allow site admin to create and modify tasks. Also changed required=True to False for history to allow history not to be written until the task is published.

from django.core.management.base import NoArgsCommand

class Command(NoArgsCommand):
    help = "Validates all installed models."

    requires_model_validation = False

    def handle_noargs(self, **options):
        self.validate(display_num_errors=True)