IPN must match regex validator (if one is provided)

InvenTree/part/migrations/0028_auto_20200203_1007.py

@@ -0,0 +1,19 @@
+# Generated by Django 2.2.9 on 2020-02-03 10:07
+
+import InvenTree.validators
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('part', '0027_auto_20200202_1024'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='part',
+            name='IPN',
+            field=models.CharField(blank=True, help_text='Internal Part Number', max_length=100, validators=[InvenTree.validators.validate_part_ipn]),
+        ),
+    ]