app/generate-migrations.php

@@ -499,6 +499,9 @@ use Phinx\Seed\AbstractSeed;
                     }
                     $value = "'{$value}'";
                 }
+                if ($value === null) {
+                    $value = 'null';
+                }
                 $output []= "\t\t\t\t'{$key}' => {$value},";
             }
             $output []= "\t\t\t],";