Fix for string form fields (#10814)

* Fix for string form fields

- replace null values with empty strings

* Expose more serializer metadata

* Check if null values are not allowed

* Fix type

* Try removing feature

* Reduce deltas

* Remove extra field attrs entirely (for testing)

* Comment out changes

* Tweak form values

* Fix for form validation

src/backend/InvenTree/InvenTree/metadata.py

@@ -420,6 +420,13 @@ class InvenTreeMetadata(SimpleMetadata):
         if field_info['type'] == 'dependent field':
             field_info['depends_on'] = field.depends_on
 
+        # Extends with extra attributes from the serializer
+        extra_field_attributes = ['allow_blank', 'allow_null']
+
+        for attr in extra_field_attributes:
+            if hasattr(field, attr):
+                field_info[attr] = getattr(field, attr)
+
         # Extend field info if the field has a get_field_info method
         if (
             not field_info.get('read_only')