Fix none access_token

jet/dashboard/dashboard_modules/google_analytics.py

@@ -146,7 +146,7 @@ class CredentialWidget(Widget):
             'type': 'hidden',
             'name': 'credential',
         })
-        attrs['value'] = force_unicode(value)
+        attrs['value'] = force_unicode(value) if value else ''
 
         return format_html('%s<input{} />' % link, flatatt(attrs))
 

jet/dashboard/dashboard_modules/yandex_metrika.py

@@ -99,6 +99,10 @@ class AccessTokenWidget(Widget):
             link = '<a href="%s">Revoke access</a>' % reverse('jet-dashboard:yandex-metrika-revoke', kwargs={'pk': self.module.model.pk})
         else:
             link = '<a href="%s">Grant access</a>' % reverse('jet-dashboard:yandex-metrika-grant', kwargs={'pk': self.module.model.pk})
+
+        if value is None:
+            value = ''
+
         return format_html('%s<input type="hidden" name="access_token" value="%s">' % (link, value))