django.db.utils.OperationalError: (1067, "Invalid default value for 'age'") - Deploying Pug or Ugh API App

from django.contrib.auth.models import User
from django.db import models
from django.db.models.signals import post_save


class Dog(models.Model):
    """Dog model class."""
    GENDER_CHOICES = (
        ('m', 'male'),
        ('f', 'female'),
        ('u', 'unknown'),
    )
    SIZE_CHOICES = (
        ('s', 'small'),
        ('m', 'medium'),
        ('l', 'large'),
        ('xl', 'extra large'),
        ('u', 'unknown'),
    )

    name = models.CharField(max_length=255, default='Unknown name')
    image_filename = models.CharField(max_length=255, default='')
    breed = models.CharField(max_length=255, default='Unknown mix')
    age = models.IntegerField(default=1, blank=True, null=True)
    gender = models.CharField(
        max_length=1,
        choices=GENDER_CHOICES,
        default='Unknown gender'
    )
    size = models.CharField(
        max_length=2,
        choices=SIZE_CHOICES,
        default='Unknown size'
    )
    neutered = models.BooleanField(default=False)

    def __str__(self):
        return self.name