added functionality to Serializer validate method

Sistemas/migrations/0007_alter_device_sistema.py

@@ -0,0 +1,19 @@
+# Generated by Django 4.1.3 on 2023-01-25 14:33
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('Sistemas', '0006_device_sistema'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='device',
+            name='sistema',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, to='Sistemas.sistema'),
+        ),
+    ]