Url fix 2 (#9548) (#9550)

* Logic fix

* Playwright test

* Revert "Playwright test"

This reverts commit a63b239.

* Simplify test

* Cleanup test

Author: SchrodingersGat

src/backend/InvenTree/InvenTree/fields.py

@@ -38,7 +38,7 @@ def run_validation(self, data=empty):
 
         if not strict_urls and data is not empty and data is not None:
             data = str(data).strip()
-            if '://' not in data:
+            if data and '://' not in data:
                 # Validate as if there were a schema provided
                 data = 'http://' + data