djangae ImageField tidak bekerja dengan CloudStorage

saya menggunakan Djangae untuk menjalankan aplikasi saya di google appengine, saya mencoba menyimpan gambar ke google CloudStorage,

saya mengikuti proses yang sama persis seperti yang disebutkan di sini tetapi tidak ada yang tertulis di dalamnya CloudStorage, tidak ada kesalahan, tidak ada pengecualian!

ini adalah kelas model yang saya miliki:

class Person(models.Model):
    user = models.ForeignKey(User, default=1)
    name = models.CharField(max_length=250,null=True)
    last_name = models.CharField(max_length=500)
    age= models.IntegerField(default=100)
    martial_status = models.CharField(max_length=20, choices=STATUS_CHOICES, default=("Single"))
    sex = models.CharField(max_length=20, choices=SEX_CHOICES, default=("Male"))
    mobile=models.CharField(max_length=26,default=0011)
    amount_paid=models.CharField(max_length=256,null=True)
    amount_left = models.CharField(max_length=256, null=True,blank=True)
    note=models.CharField(max_length=256,null=True,blank=True)
    address=models.CharField(max_length=256,null=True,blank=True)
    date = models.DateField(("Date"), default=date.today,blank=True)
    chief_complain = models.CharField(max_length=256,null=True,blank=True)
    treatment_plan=models.CharField(max_length=256,null=True,blank=True)
    treatment_done=models.CharField(max_length=256,null=True,blank=True)
    #picture = models.ImageField(blank=True)
    picture = models.ImageField(upload_to='/image/', storage=public_storage,blank=True)
    def __str__(self):
        return self.name

Bentuk Model :

class PersonForm(forms.ModelForm):

    class Meta:
        model = Person
        fields = ['name', 'last_name', 'age', 'martial_status', 'mobile', 'sex',
                  'amount_paid','amount_left','note', 'address','date','picture','treatment_done','treatment_plan','chief_complain']
        widgets = {
            'name': forms.TextInput(attrs={'required': True, 'class': 'form-control',
                                             'placeholder': 'name'}),
            'last_name': forms.TextInput(attrs={'required': True, 'class': 'form-control',
                                           'placeholder': 'lastname'}),
            'age': forms.TextInput(attrs={'required': True, 'class': 'form-control',
                                           'placeholder': 'age'}),
            'amount_paid': forms.TextInput(attrs={'required': True, 'class': 'form-control',
                                           'placeholder': 'amount paid'}),
            'amount_left': forms.TextInput(attrs={'required': True, 'class': 'form-control',
                                           'placeholder': 'amount left'}),
            'note': forms.TextInput(attrs={'required': False, 'class': 'form-control',
                                           'placeholder': 'Patient History'}),
            'address': forms.TextInput(attrs={'required': False, 'class': 'form-control',
                                           'placeholder': 'Current address'}),
            'chief_complain': forms.TextInput(attrs={'required': False, 'class': 'form-control',
                                           'placeholder': 'chief complain'}),
            'treatment_plan': forms.Textarea(attrs={'required': False, 'class': 'form-control',
                                           'placeholder': 'treatment plan','rows':'3'}),
            'treatment_done': forms.Textarea(attrs={'required': False, 'class': 'form-control',
                                           'placeholder': 'treatment done','rows':'3'}),




        }

templatnya:

<h2>Add person</h2>
  <form method="post">
    {% csrf_token %}


<div class="row">
     <div class="col-sm-4 form-group">
       <label for="name" >{% trans "Name" %}</label>
       {{ form.name|add_class:"form-control" }}
      </div>

..<code snippet>..

      <div class="row">
       <div class="col-sm-4 form-group">
       <label for="address">{% trans "Address" %}</label>
       {{ form.address|add_class:"form-control" }}
      </div>
          <div class="col-sm-4 form-group">
       <label for="pic">{% trans "Picture" %}</label>
        {{form.picture}}
      </div>
      </div>