Allow null values for integer columns

Author: Jeroen

lib/internal/Magento/Framework/Setup/Declaration/Schema/Dto/Factories/Integer.php

@@ -63,7 +63,7 @@ public function create(array $data)
         }
 
         if (isset($data['default'])) {
-            $data['default'] = (int) $data['default'];
+            $data['default'] = $data['default'] !== 'null' ? (int) $data['default'] : null;
         }
 
         return $this->objectManager->create($this->className, $data);

lib/internal/Magento/Framework/Setup/Declaration/Schema/etc/types/integers/integer.xsd

@@ -17,7 +17,13 @@
                         Size is 4 bytes.
                     </xs:documentation>
                 </xs:annotation>
-                <xs:attribute name="default" type="xs:integer" />
+                <xs:attribute name="default">
+                    <xs:simpleType>
+                        <xs:restriction base="xs:string">
+                            <xs:pattern value="\d+|null" />
+                        </xs:restriction>
+                    </xs:simpleType>
+                </xs:attribute>
                 <xs:attribute name="padding">
                     <xs:annotation>
                         <xs:documentation>