Support non-integer serial numbers

InvenTree/stock/migrations/0050_auto_20200821_1403.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.0.7 on 2020-08-21 14:03
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stock', '0049_auto_20200820_0454'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='stockitem',
+            name='serial',
+            field=models.CharField(blank=True, help_text='Serial number for this item', max_length=100, null=True, verbose_name='Serial Number'),
+        ),
+    ]