Error when trying to create a new BomItem
1. Try to create new BomItem for a Part
2. Leave the `sub_part` field blank
3. Submit form

The form errors out in the `BomItem.clean()` function..


diff --git a/InvenTree/build/models.py b/InvenTree/build/models.py
index 92f04bdcc..b5f5aa10e 100644
--- a/InvenTree/build/models.py
+++ b/InvenTree/build/models.py
@@ -17,7 +17,7 @@ from django.db.models import Sum
 from django.core.validators import MinValueValidator
 
 from stock.models import StockItem
-from part.models import BomItem
+from part.models import Part, BomItem
 
 
 class Build(models.Model):
@@ -368,15 +368,21 @@ class BuildItem(models.Model):
 
         errors = {}
 
-        if self.stock_item is not None and self.stock_item.part is not None:
+        try:
             if self.stock_item.part not in self.build.part.required_parts():
                 errors['stock_item'] = [_("Selected stock item not found in BOM for part '{p}'".format(p=self.build.part.full_name))]
             
-        if self.stock_item is not None and self.quantity > self.stock_item.quantity:
-            errors['quantity'] = [_("Allocated quantity ({n}) must not exceed available quantity ({q})".format(
-                n=self.quantity,
-                q=self.stock_item.quantity
-            ))]
+            if self.quantity > self.stock_item.quantity:
+                errors['quantity'] = [_("Allocated quantity ({n}) must not exceed available quantity ({q})".format(
+                    n=self.quantity,
+                    q=self.stock_item.quantity
+                ))]
+
+        except StockItem.DoesNotExist:
+            pass
+
+        except Part.DoesNotExist:
+            pass
 
         if len(errors) > 0:
             raise ValidationError(errors)
diff --git a/InvenTree/part/models.py b/InvenTree/part/models.py
index 8383431ca..385bae7bf 100644
--- a/InvenTree/part/models.py
+++ b/InvenTree/part/models.py
@@ -858,13 +858,19 @@ class BomItem(models.Model):
         """
 
         # A part cannot refer to itself in its BOM
-        if self.part == self.sub_part:
-            raise ValidationError({'sub_part': _('Part cannot be added to its own Bill of Materials')})
-
-        # Test for simple recursion
-        for item in self.sub_part.bom_items.all():
-            if self.part == item.sub_part:
-                raise ValidationError({'sub_part': _("Part '{p1}' is  used in BOM for '{p2}' (recursive)".format(p1=str(self.part), p2=str(self.sub_part)))})
+        try:
+            if self.sub_part is not None and self.part is not None:
+                if self.part == self.sub_part:
+                    raise ValidationError({'sub_part': _('Part cannot be added to its own Bill of Materials')})
+        
+            # Test for simple recursion
+            for item in self.sub_part.bom_items.all():
+                if self.part == item.sub_part:
+                    raise ValidationError({'sub_part': _("Part '{p1}' is  used in BOM for '{p2}' (recursive)".format(p1=str(self.part), p2=str(self.sub_part)))})
+        
+        except Part.DoesNotExist:
+            # A blank Part will be caught elsewhere
+            pass
 
     class Meta:
         verbose_name = "BOM Item"
['InvenTree/part/models.py', 'InvenTree/build/models.py']