Fix issue where Decimal value block null caused an error

- Fixes #9777
- DecimalBlock value when Null forces a conversion to null which crashes the server. Fixed it by returning null when the value is null and decimal when a value is other than null

CHANGELOG.txt

@@ -48,6 +48,7 @@ Changelog
  * Fix: Use the correct padding for autocomplete block picker (Umar Farouk Yunusa)
  * Fix: Ensure that short content pages (such as editing snippets) do not show an inconsistent background (Sage Abdullah)
  * Fix: Fix horizontal positioning of rich text inline toolbar (Thibaud Colas)
+ * Fix: Ensure that `DecimalBlock` correctly handles `None`, when `required=False`, values (Natarajan Balaji)
  * Docs: Add custom permissions section to permissions documentation page (Dan Hayden)
  * Docs: Add documentation for how to get started with contributing translations for the Wagtail admin (Ogunbanjo Oluwadamilare)
  * Docs: Officially recommend `fnm` over `nvm` in development documentation (LB (Ben) Johnston)

CONTRIBUTORS.rst

@@ -675,6 +675,7 @@ Contributors
 * Jeremy Thompson
 * Ben Gosney
 * damascene
+* Natarajan Balaji
 
 Translators
 ===========

docs/releases/4.2.md

@@ -62,6 +62,7 @@ Wagtail now provides a set of utilities for creating data migrations on StreamFi
  * Use the correct padding for autocomplete block picker (Umar Farouk Yunusa)
  * Ensure that short content pages (such as editing snippets) do not show an inconsistent background (Sage Abdullah)
  * Fix horizontal positioning of rich text inline toolbar (Thibaud Colas)
+ * Ensure that `DecimalBlock` correctly handles `None`, when `required=False`, values (Natarajan Balaji)
 
 ### Documentation
 

wagtail/blocks/field_block.py

@@ -251,7 +251,10 @@ class DecimalBlock(FieldBlock):
         super().__init__(*args, **kwargs)
 
     def to_python(self, value):
-        return Decimal(value)
+        if value is None:
+            return value
+        else:
+            return Decimal(value)
 
     class Meta:
         icon = "plus-inverse"

wagtail/tests/test_blocks.py

@@ -419,6 +419,11 @@ class TestDecimalBlock(TestCase):
         )  # decimals get saved as string in JSON field
         self.assertEqual(type(block_val), Decimal)
 
+    def test_type_to_python_decimal_none_value(self):
+        block = blocks.DecimalBlock()
+        block_val = block.to_python(None)
+        self.assertIsNone(block_val)
+
     def test_render(self):
         block = blocks.DecimalBlock()
         test_val = Decimal(1.63)