如何检查ImageField是空的

from django.core.files.storage import default_storage
from django.core.exceptions import ValidationError
from django.core.validators import URLValidator

def check_image_field_empty(image_field):
    if image_field is None:
        return True
    return False

def check_image_field_url_valid(image_field):
    if image_field is None:
        return False
    validator = URLValidator()
    try:
        validator(image_field.url)
        return True
    except ValidationError:
        return False

def check_image_field_exists(image_field):
    if image_field is None:
        return False
    storage, path = default_storage.url(image_field.url).split('/', 1)
    return default_storage.exists(path)